EXCLUSIVE: Natalie Cole's sisters open up about their last days with the legendary singer

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EXCLUSIVE: Natalie Cole's Sisters Reveal Why She Kept Her Illness a Secret

Following Natalie Cole's death, ET sat down with her sisters Timolin and Casey, who revealed why their sister suffered in secret.

The legendary singer was embattled with health issues for years before dying from congestive heart failure on Dec. 31 in a Los Angeles hospital, but kept silent about her illnesses. Casey told ET that Natalie treasured her privacy and didn't want to draw too much attention.

SEE MORE: Natalie Cole Dead at 65

"She was very protective of her family and her close friends, and I don't think that she wanted people to start feeling sorry for her," Casey said. "She really thought and prayed that she would overcome this."

The "Unforgettable" singer wowed the world with her talent, winning multiple GRAMMYs in her career, but she also had a drug-addled past. In 2007, she was diagnosed with Hepatitis C and had a kidney transplant in 2009.

Following the kidney transplant, Natalie began to experience complications with her heart and her siblings told ET that they knew this Christmas would be her last.

See photos of Natalie Cole from throughout her life:

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EXCLUSIVE: Natalie Cole's sisters open up about their last days with the legendary singer
06/30/2005.gala.Natalie Cole performs one of threee songs at the gala. A black tie Inagural Gala was held this evening at the Dorothy chandler Pavilion in Los Angeles for Mayor elect Antonio Villaraigosa, who will be sworn in tomorrow. Dinner and dancing was held by the fountain outdoors in the huge fundraising affair. (Photo by Anne Cusack/Los Angeles Times via Getty Images)
ATLANTA, GA - JUNE 26: Recording Artist Natalie Cole performs atJazz 91.9 WCLK 41st Anniversary Benefit Concert at Cobb Energy Performing Arts Center on June 26, 2015 in Atlanta, Georgia. (Photo by Moses Robinson/Getty Images)
ATLANTA, GA - JUNE 26: Recording Artist Natalie Cole performs atJazz 91.9 WCLK 41st Anniversary Benefit Concert at Cobb Energy Performing Arts Center on June 26, 2015 in Atlanta, Georgia. (Photo by Moses Robinson/Getty Images)
BRENTWOOD, CA - JUNE 11: Recording artist Natalie Cole performs onstage during City Of Hope's 11th Annual 'Songs Of Hope' Event on June 11, 2015 in Brentwood, California. (Photo by Lester Cohen/Getty Images for City of Hope)
LOS ANGELES, CA - FEBRUARY 22: Singer Natalie Cole attends Mercedes-Benz USA and African American Film Critics Association Academy Awards viewing party on February 22, 2015 in Los Angeles, California. (Photo by Chelsea Lauren/Getty Images for Mercedes-Benz USA)
NEW YORK, NY - OCTOBER 20: Natalie Cole attends Angel Ball 2014 hosted by Gabrielle's Angel Foundation at Cipriani Wall Street on October 20, 2014 in New York City. (Photo by Jamie McCarthy/Getty Images for Gabrielle's Angel Foundation)
BEVERLY HILLS, CA - OCTOBER 11: Recording artists Johnny Mathis (L) and Natalie Cole attend the 2014 Carousel of Hope Ball presented by Mercedes-Benz at The Beverly Hilton Hotel on October 11, 2014 in Beverly Hills, California. (Photo by Kevin Winter/Getty Images)
BERLIN, GERMANY - JULY 16: American singer Natalie Cole performs live during a concert at the Admiralspalast on July 16, 2014 in Berlin, Germany. (Photo by Frank Hoensch/Redferns via Getty Images)
CIRCA 1955: Singer Nat 'King' Cole and his daughter Natalie Cole pose for a portrait session in front of a Christmas tree in circa 1955. (Photo by Michael Ochs Archives/Getty Images)
CIRCA 1955: Singer Nat 'King' Cole and his daughter Natalie Cole pose for a portrait session in front of a Christmas tree in circa 1955. (Photo by Michael Ochs Archives/Getty Images)
CANADA - CIRCA 1900: Natalie Cole (Photo by Toronto Star Archives/Toronto Star via Getty Images)
UNSPECIFIED - CIRCA 1970: Photo of Natalie Cole Photo by Michael Ochs Archives/Getty Images
UNSPECIFIED - CIRCA 1970: Photo of Natalie Cole Photo by Michael Ochs Archives/Getty Images
UNSPECIFIED - CIRCA 1970: Photo of Natalie Cole Photo by Michael Ochs Archives/Getty Images
Publicity shots of the singer Natalie Cole, 1992. (Photo by Afro American Newspapers/Gado/Getty Images)
American singer Natalie Cole, 1975. Daughter of Nat King Cole. (Photo by Afro American Newspapers/Gado/Getty Images)
UNSPECIFIED - CIRCA 1970: Photo of Natalie Cole Photo by Michael Ochs Archives/Getty Images
UNSPECIFIED - CIRCA 1970: Photo of Natalie Cole Photo by Michael Ochs Archives/Getty Images
UNSPECIFIED - CIRCA 1970: Photo of Natalie Cole Photo by Michael Ochs Archives/Getty Images
HOLLYWOOD - FEBRUARY 19: Singer Natalie Cole and guests attending 19th Annual Grammy Awards on February 19, 1977 at Hollywood Palladium in Hollywood, California. (Photo by Ron Galella/WireImage)
1978 AMERICAN MUSIC AWARDS - Gallery - Shoot Date: November 18, 1977. (Photo by ABC Photo Archives/ABC via Getty Images) HOSTS DAVID SOUL AND NATALIE COLE
NEW YORK CITY - AUGUST 5: Singer Natalie Cole autographing new album 'Unforgettable With Love' on August 5, 1992 at Sam Goody's in New York City, New York. (Photo by Ron Galella, Ltd./WireImage)
NEW YORK CITY - AUGUST 5: Singer Natalie Cole autographing new album 'Unforgettable With Love' on August 5, 1992 at Sam Goody's in New York City, New York. (Photo by Ron Galella, Ltd./WireImage)
NEW YORK, NY Â FEB 25: Natalie Cole attends the 34th Annual Grammy Awards at Radio City Music Hall on Feb 25, 1992 in New York City. (Photo by Robin Platzer/Images/Getty Images)
(GERMANY OUT) e, Natalie *06.02.1950-Saengerin, USA- Konzert in der Philharmonie in Berlin- Mai 1992 (Photo by POP-EYE/ullstein bild via Getty Images)
Natalie Cole performs on stage at RAI Congrescentrum, Amsterdam, Netherlands, 10th May 1992. (Photo by Rob Verhorst/Redferns)
Portrait of singer Natalie Cole, 1993. (Photo by Afro American Newspapers/Gado/Getty Images)
Singer/songwriter Natalie Cole, right, walks off stage after receiving "The Hitmaker's Award" from legendary vocalist Tony Bennett, at the Songwriter's Hall of Fame Wednesday, June 9, 1999, in New York. Cole is the daughter of the late vocalist Nat King Cole. (AP Photo/Stuart Ramson)
Natalie Cole's Grammy-winning compact disk, "Unforgettable," in its jewel box, right, is dwarfed by the "long box" packaging that it is currently available in at a New York music store, Thursday, February 27, 1992. The Recording Industry Association of America announced Thursday that it would adopt a new packaging standard that would eliminate the long box by April 1993 and instead make use of only the 5"x 5 1/2" jewel box. (AP Photo/Mark Phillips)
Ray Charles talks about Nat King Cole as Cole's daughter Natalie looks on backstage the 15th Annual Rock and Roll Hall of Fame Induction Dinner Monday, March 6, 2000, at New York's Waldorf-Astoria. Ray Charles presented Nat King Cole's award to his three daughters. (AP Photo/Ed Betz)
Natalie Cole performs in a '70s afro wig during the "13th Annual Race to Erase M.S." fashion show/concert at the Century Plaza Hotel in Los Angeles, Friday, May 12, 2006. The charity event was themed "Disco Fever to Erase M.S." (AP Photo/Chris Pizzello)
Natalie Cole sings for Los Angeles Mayor-elect Antonio Villaraigosa during his inaugural gala in Los Angeles on Thursday, June 30, 2005. Villaraigosa is to be sworn in on Friday. (AP Photo/Chris Carlson)
Tony Bennett, right, greets Natalie Cole with a kiss before they sang a duet with at a 106.7 Lite fm ?One Night With Lite? Concert at The Theater at Madison Square Garden, Tuesday, Sept. 26, 2006 in New York. (AP Photo/Henny Ray Abrams)
U.S. jazz singer Natalie Cole performs during her concert at the Torwar arena in Warsaw, Poland, Monday, July 16, 2007. The concert was a part of the Warsaw Summer Jazz Days festival. (AP Photo/Alik Keplicz)
Natalie Cole arrives for the 49th Annual Grammy Awards on Sunday, Feb. 11, 2007, in Los Angeles. (AP Photo/Matt Sayles)
Singer Natalie Cole attends the 2007 G&P Foundation 10th Annual Angel Ball at the Marriott Marquis, Moday, Oct. 29, 2007 in New York. (AP Photo/Evan Agostini)
Natalie Cole, who was recently treated for Hepatitis C, holds up a greeting card from actor/comedian George Lopez during a signing session for her new CD, "Still Unforgettable," at Borders Westwood in Los Angeles., Tuesday, Oct. 28, 2008. (AP Photo/Chris Pizzello)
Natalie Cole holds the best instrumental arrangement accompanying vocalist award backstage at the 51st Annual Grammy Awards on Sunday, Feb. 8, 2009, in Los Angeles.(AP Photo/Matt Sayles)
Singer Natalie Cole performs at the LA Live entertainment complex holiday tree lighting ceremony in Los Angeles on Thursday, Dec. 4, 2008. (AP Photo/Dan Steinberg)
075207.CA.1220.baltin.cc Natalie Cole, was one of the maney articts performing at the Stevie Wonder's Eighth Annual House Full of Toys Benefite Concert held at The Forum Saturday night. (Photo by Carlos Chavez/Los Angeles Times via Getty Images)
American singer, and songwriter, Natalie Cole, 23rd October 1975. (Photo by Michael Putland/Getty Images)
1978 AMERICAN MUSIC AWARDS - Broadcast Coverage - Airdate: January 16, 1978. (Photo by ABC Photo Archives/ABC via Getty Images) HOST NATALIE COLE
(GERMANY OUT) e, Natalie *06.02.1950-Saengerin, USA- Konzert in der Philharmonie in Berlin- Mai 1992 (Photo by POP-EYE/ullstein bild via Getty Images)
Natalie Maria Cole, an African-American singer, songwriter, and performer, and the daughter of Nat King Cole, on television with another person, mid to late twentieth century. (Photo by Afro American Newspapers/Gado/Getty Images)
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SEE MORE: Natalie Cole on Singing Duets With Late Father

"When we came to the hospital and spent Christmas Eve with her it was a godsend," Timolin said. "We were very blessed and thankful to spend that very special day with her that she loved. It was her favorite time of year."

Natalie is survived by her 38-year-old son, Robert Yancy, who Timolin says was "very close" to his mom.

"He is having a hard time," she said. "I think it's going to be a process."

Natalie's family is keeping her spirit alive through the Nat King Cole Generation Hope organization, which provides music education to children in need.

SEE MORE: Smokey Robinson Remembers Natalie Cole

Former ET host Mary Hart helped remember Natalie by reflecting on the time she spent with her in 2008, when Natalie was still in need of a new kidney.

"I'm a survivor," Natalie said at the time. "I don't know where I really got it from, but I just don't believe in giving up until the fat lady sings, and the fat lady hasn't sung yet."

Singer Natalie Cole Dead at 65
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