Sean Astin says mother Patty Duke was 'suffering terribly' before her death

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EXCLUSIVE: Sean Astin Says Mother Patty Duke Was 'Suffering Terribly'

Sean Astin was with his mother, Anna "Patty Duke" Pearce, when she died on Tuesday morning and he shared her final moments with ET in his only on-camera interview.

"She was surrounded by her family," Astin told ET. "It was in the middle of the night and it was a race to get there. It was a very powerful experience. And then, in her last moments, she was at peace."

WATCH: Sean Astin Remembers Late Mother Patty Duke

Her peace came after a painful battle with sepsis due to a ruptured intestine.

"She had been suffering terribly," Astin said.

Patty Duke through the years:

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Patty Duke through the years
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Sean Astin says mother Patty Duke was 'suffering terribly' before her death
Child actress Patty Duke roller skates in Central Park in New York City, April 6, 1961. (AP Photo)
Gregory Peck, holding pocket watch, jokes with, from left, Patty Duke, Joan Crawford and Ed Begley backstage at the Academy Awards at Santa Monica Civic Auditorium in Los Angeles, Ca., April 8, 1963. Peck won best actor for "To Kill a Mockingbird"; Duke won best supporting actress for "The Miracle Worker"; Crawford accepted the Oscar for Anne Bancroft, who won best actress for "The Miracle Worker"; and Begley won best supporting actor for "Sweet Bird of Youth." (AP Photo)
Child actress Patty Duke is filling out the letters of her name as it appears on the marquee at the Playhouse Theatre in New York City, advertising the play "The Miracle Worker," on March 25, 1960. 13-year-old Patty, who stars opposite Anne Bancroft in the hit show, is held and supported by Mannie Kay, president of the sign company. (AP Photo)
Actress Patty Duke, star of ABC-TV's "The Patty Duke Show," and Colette Daiute, right, who recently won the Miss Teenage America contest, meet at a Hollywood beauty salon as they prepare for their roles on Patty's show, Dec. 3, 1965. Fixing Patty's hair is hair stylist Jeanne Bodel. (AP Photo)
Winners of the best supporting performers Oscars pose with the presenters at the annual Academy Awards at Santa Monica, Ca., on April 8, 1963. Left to right; presenter George Chakiris, Patty Duke who won the best supporting actress for her role in The Miracle Worker, Ed Begley, names best supporting actor for the Sweet Bird of Youth, and Rita Moreno who presented Begley with his Oscar. (AP Photo)
UNITED STATES - NOVEMBER 12: JOURNEY TO THE UNKNOWN - 'Last Visitor' 6/16/69 Patty Duke (Photo by ABC Photo Archives/ABC via Getty Images)
UNITED STATES - NOVEMBER 12: JOURNEY TO THE UNKNOWN - 'Last Visitor' 6/16/69 Patty Duke (Photo by ABC Photo Archives/ABC via Getty Images)
LOS ANGELES, CA - FEBRUARY 2: Patty Duke attends 27th Annual Golden Globe Awards on February 2, 1970 at the Ambassador Hotel in Los Angeles, California. (Photo by Ron Galella, Ltd./WireImage)
LOS ANGELES, CA - FEBRUARY 2: Patty Duke attends 27th Annual Golden Globe Awards on February 2, 1970 at the Ambassador Hotel in Los Angeles, California. (Photo by Ron Galella, Ltd./WireImage)
Patty Duke during 27th Annual Golden Globe Awards at Ambassador Hotel in Los Angeles, California, United States. (Photo by Ron Galella/WireImage)
Actress Patty Duke appears as a witness before a House Appropriations Subcomittee holding hearings on funding for mental health programs on Capitol Hill in Washington, D.C., April 27, 1989. At left is chairman of the panel Rep. William Natcher of Kentucky. (AP Photo/Dennis Cook)
CANADA - JULY 25: Patty Duke's childhood of sorrows. 'Perfect teen' image hid tale of exploitation and abouse/H1 (Photo by Andrew Stawicki/Toronto Star via Getty Images)
John Astin and Patty Duke during 'Hedda Gabler' Los Angeles Premiere at Huntington Hartford Theater in Hollywood, California, United States. (Photo by Ron Galella/WireImage)
MARCUS WELBY, M.D. - 'Unindicted Wife' - Aired on February 25, 1975. (Photo by ABC Photo Archives/ABC via Getty Images) JOHN ASTIN;PATTY DUKE
FILE - In this Aug. 17, 2004 file photo, actress Patty Duke is honored with a star on the Hollywood Walk of Fame in Los Angeles.Duke, who won an Oscar as a child at the start of an acting career that continued through her adulthood, died Tuesday, March 29, 2016, of sepsis from a ruptured intestine. She was 69. (AP Photo/Damian Dovarganes, File)
Award-winning actress Patty Duke poses for photographers with her granddaughters, 2-year-old Elizabeth Astin (L) and 7-year-old Alexandra Astin following an unveiling ceremony, honoring Duke with the 2,260th star on the Hollywood Walk of Fame in Los Angeles, California August, 17, 2004. Duke won the Oscar for best supporting actress for "The Miracle Worker" at 16, the youngest at the time to be so named. REUTERS/Jim Ruymen JR/GN
HOLLYWOOD - AUGUST 17: Actor David Ogden Stiers kisses actress Patty Duke at the ceremony honoring Duke with a star on the Hollywood Walk of Fame August 17, 2004 in Hollywood, California. (Photo by Vince Bucci/Getty Images)
Award-winning actress Patty Duke (C) poses with sons, MacKenzie (L) and Sean Astin following an unveiling ceremony honoring Duke with the 2,260th star on the Hollywood Walk of Fame in Los Angeles, California August, 17, 2004. Duke won the Oscar for best supporting actress for "The Miracle Worker," at 16, the youngest at the time to be so named. REUTERS/Jim Ruymen JR
Patty Duke during Patty Duke Honored with a Star on the Hollywood Walk of Fame for Her Achievements in Film at 7000 Hollywood Blvd. in Hollywood, California, United States. (Photo by Jesse Grant/WireImage)
Actress Patty Duke is seen during an interview in New York, Nov. 18, 2002. Duke, Helen Keller in "The Miracle Worker," 1960s TV icon and pill-popping heroine of "Valley of the Dolls," has joined the cast of the Broadway revival of "Oklahoma!" (AP Photo/Louis Lanzano)
Academy and Emmy award-winning actress, Patty Duke is shown during a news conference at the Paley Center for Media in Beverly Hills, Calif., on Tuesday, March 23, 2010. The cast of the 1960s TV comedy "The Patty Duke Show," are promoting the Social Security Administration's service allowing baby boomers to apply online for retirement and Medicare benefits. (AP Photo/Damian Dovarganes)
The cast of the television hit 1960s sitcom: âThe Patty Duke Show," Paul O'Keefe, left, and Patty Duke, smile during a Social Security news conference at the Paley Center for Media in Beverly Hills, Calif., on Tuesday, March 23, 2010. The cast of the 1960s TV comedy now as seasoned citizens, are promoting the Social Security Administration's service allowing baby boomers to apply online for retirement and Medicare benefits. (AP Photo/Damian Dovarganes)
Patty Duke speaks at the national premiere of her new Social Security Public Service Snnouncement at the Paley Center for Media in New York City. January 6, 2009 Credit: Dennis Van Tine/MediaPunch/IPX
HOLLYWOOD, CA - MARCH 7: Actress Patty Duke Astin receives her award for Favorite Dual-Role on stage at the 2nd Annual TV Land Awards held on March 7, 2004 at The Hollywood Palladium, in Hollywood, California. (Photo by Kevin Winter/Getty Images)
Actress Patty Duke talks about working on a student production of 'The Four Children of Tander Welch,' in Columbia, South Carolina, on November 20, 2006. (Photo by Gerry Melendez/The State/MCT via Getty Images)
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Duke died at the age of 69 at a hospital in Coeur D'Alene, Idaho. She was perhaps best known for portraying Helen Keller in 1962's The Miracle Worker, a role that earned her an Academy Award for Best Supporting Actress. At the time, she was the youngest Oscar winner ever at 16.

WATCH: Melissa Gilbert Remembers Patty Duke After Her Death: 'She Was My Second Mom'

Along with her Oscar win, she will also be remembered for helping destigmatize mental illness. After bravely going public about her struggle with manic depression, Duke traveled the nation lobbying as a mental health advocate.

"The more she opened up, the more she shared of her pain. It is very instructive for people," Astin said. "This [1982] bipolar diagnosis was a watershed. Now she had a new identity and a whole new mission -- a whole new sense of purpose -- and that was to share what she had gone through with other people."

The actress, along with other advocates like former First Lady Rosalynn Carter and Mariel Hemingway, spoke out publicly about her bipolar disorder and other psychiatric health issues at a time when mental illnesses carried an even heavier stigma. Duke even opened up to ET about her diagnosis in a 1992 interview.

"I happen to prefer calling my disorder manic depression," Duke told ET at the time. "It is known as bipolar now. And if that works for other people, fine, but I prefer to call it manic depression because it sounds like it felt."

WATCH: Patty Duke Dies at 69 -- Hollywood Pays Tribute

To honor his mother's legacy, Astin has set up a fundraiser for The Patty Duke Mental Health Project, which will continue Duke's campaign of awareness.

"Above all, the way that I think of my mother, the thing that gives me such joy and reverence for her, is that above all else, she was a warrior," Astin said.

Notable people we lost in 2016:

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Notable people we lost in 2016 (deaths)
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Sean Astin says mother Patty Duke was 'suffering terribly' before her death

January 1 -- Former U.S. Sen. Dale Bumpers, D-Ark., seen here in 2006, passed away at the age of 90. Bumpers' signature moment on the national stage came in 1999, just weeks after leaving the Senate, when he defended Pres. Bill Clinton — who had worked for a challenger's 1974 campaign — before the U.S. Senate during his impeachment trial.

(AP Photo/Danny Johnston)

January 4 -- Robert Stigwood, manager of the Bee Gees and Cream.

(Photo by Michael Putland/Getty Images)

January 4 -- Country singer Craig Strickland was found dead at age 29 from hypothermia.

(Photo via Instagram)

January 6 -- Pat Harrington, Jr., actor in 'One Day at a Time,' died at 86 from complications from Alzheimer's disease.

(Photo by CBS via Getty Images)

January 11 -- Singer David Bowie died after battling cancer for 18 months. He was 69.

(AP Photo/Marty Lederhandler, FIle)

January 14 -- Actor Alan Rickman, popular for playing Professor Snape in the 'Harry Potter' films, died at 69 after battling cancer.

(Photo by Mike Pont/WireImage)

January 18 -- Glenn Frey, founding member of The Eagles, died at age 67 due to complications from multiple ailments.

(Photo by Tommaso Boddi/WireImage)

January 29 -- Paul Kantner, guitarist, vocalist and founding member of the band Jefferson Airplane, passed away at age 74 of multiple organ failure following a heart attack.

(AP Photo/Shawn Baldwin, File)

February 2 -- Jibri Bryan, #34, of the Mercer Bears was killed in a shooting at age 23.

(Photo by Streeter Lecka/Getty Images)

February 4 -- Maurice White, founder of Earth, Wind & Fire, died from the effects of Parkinson's disease at age 74.

(Photo by Richard E. Aaron/Redferns)

February 4 -- Astronaut Edgar D. Mitchell, the sixth person to walk on the moon, passed away at 85 under hospice care.

(Photo via NASA)

February 13 -- United States Supreme Court justice, Antonin Scalia.

(AP Photo/Haraz N. Ghanbari)

February 19 -- Author of the beloved novel To Kill A Mockingbird, Harper Lee.

(AP Photo, File)

March 9 -- Beatles producer Sir George Martin passed away at age 90, as announced by Ringo Starr on Twitter.

(Photo by Vince Bucci/Getty Images)

March 16 -- Singer Frank Sinatra Jr.

(Photo by Express/Express/Getty Images)

March 24 -- Comedian Garry Shandling at age 66. 

(AP Photo/Chris Carlson, File)

March 29 -- Oscar winning actress Patty Duke, at the age of 69.

(Photo by ABC Photo Archives/ABC via Getty Images) 
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