Olivia Newton-John postpones tour as she reveals she has breast cancer

Olivia Newton-John has breast cancer.

The 68-year-old star took to Facebook on Tuesday to reveal she was "reluctantly" postponing her upcoming tour dates because of the diagnosis.

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"Olivia Newton-John is reluctantly postponing her June U.S. and Canadian concert tour dates," the post read. "The back pain that initially caused her to postpone the first half of her concert tour, has turned out to be breast cancer that has metastasized to the sacrum."

Newton-John will undergo photon radiation therapy in addition to "natural wellness therapies" to combat the cancer. The post went on to say that she's "confident she will be back later in the year, better than ever, to celebrate her shows."

See photos of Olivia Newton-John:

29 PHOTOS
Olivia Newton-John out and about
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Olivia Newton-John out and about
ATLANTA, GA - APRIL 09: Olivia Newton-John performs at Cobb Energy Centre on April 9, 2017 in Atlanta, Georgia. (Photo by Chris McKay/Getty Images)
LAS VEGAS, NV - MARCH 23: Executive producer Al Bowman (L) and entertainer Olivia Newton-John, recipient of the Las Vegas Icon award, pose with her trophy during the inaugural Las Vegas F.A.M.E (Film, Art, Music and Entertainment) Awards presented by the Producers Choice Honors at the Hard Rock Cafe Las Vegas Strip on March 23, 2017 in Las Vegas, Nevada. (Photo by Gabe Ginsberg/FilmMagic)
HOLLYWOOD, CA - NOVEMBER 27: Actress / Singer Olivia Newton-John attends the 85th Annual Hollywood Christmas Parade on November 27, 2016 in Hollywood, California. (Photo by Paul Archuleta/FilmMagic)
LONDON, ENGLAND - JANUARY 26: Olivia Newton-John performs at the Union Chapel on January 26, 2017 in London, England. (Photo by Imelda Michalczyk/Redferns)
NASHVILLE, TN - NOVEMBER 02: (L-R) Hayley Orrantia, Olivia Newton-John, and Wendi McLendon-Covey appear onstage during the 50th annual CMA Awards at the Bridgestone Arena on November 2, 2016 in Nashville, Tennessee. (Photo by Taylor Hill/Getty Images)
LAS VEGAS, NV - OCTOBER 23: Entertainer Olivia Newton-John (L) and Singer Steve Real perform at a 'Turn Up the Pink' champagne brunch benefiting Making Strides Las Vegas to raise awareness and support for breast cancer research as part of the Hard Rock Cafe's Hard Rock Heals global charitable initiative at the Hard Rock Cafe Las Vegas Strip on October 23, 2016 in Las Vegas, Nevada. (Photo by Gabe Ginsberg/Getty Images)
NASHVILLE, TN - NOVEMBER 02: John Easterling and singer-songwriter Olivia Newton-John attend the 50th annual CMA Awards at the Bridgestone Arena on November 2, 2016 in Nashville, Tennessee. (Photo by Taylor Hill/Getty Images)
LAS VEGAS, NV - OCTOBER 23: Entertainer Olivia Newton-John attends 'Turn Up the Pink' champagne brunch benefiting Making Strides Las Vegas to raise awareness and support for breast cancer research as part of the Hard Rock Cafe's Hard Rock Heals global charitable initiative at the Hard Rock Cafe Las Vegas Strip on October 23, 2016 in Las Vegas, Nevada. (Photo by Gabe Ginsberg/Getty Images)
THE TONIGHT SHOW STARRING JIMMY FALLON -- Episode 0547 -- Pictured: Singer Olivia Newton-John with The Roots on October 4, 2016 -- (Photo by: Andrew Lipovsky/NBC/NBCU Photo Bank via Getty Images)
TODAY -- Pictured: (l-r) Anchors Hoda Kotb and Kathie Lee Gifford with Olivia Newton-John on Tuesday, October 4, 2016 -- (Photo by: Heidi Gutman/NBC NewsWire via Getty Images/NBCU Photo Bank via Getty Images)
NEW YORK, NY - OCTOBER 04: Singer-songwriter/actress Olivia Newton-John attends the 'Divorce' New York Premiere at SVA Theater on October 4, 2016 in New York City. (Photo by Gilbert Carrasquillo/FilmMagic)
WATCH WHAT HAPPENS LIVE -- Pictured (l-r): Cynthia Nixon and Olivia Newton-John -- (Photo by: Charles Sykes/Bravo/NBCU Photo Bank via Getty Images)
WATCH WHAT HAPPENS LIVE -- Pictured: Olivia Newton-John -- (Photo by: Charles Sykes/Bravo/NBCU Photo Bank via Getty Images)
NEW YORK, NY - OCTOBER 04: Sarah Jessica Parker and Olivia Newton-John attend 'Divorce' New York Premiere on October 4, 2016 in New York City. (Photo by Astrid Stawiarz/Getty Images)
NEW YORK, NY - OCTOBER 03: Singer Olivia Newton-John attends The Build Series Presents Olivia Newton-John, Amy Sky And Beth Nielsen Chapman to discuss The New Project 'LIV ON' at AOL HQ on October 3, 2016 in New York City. (Photo by Desiree Navarro/WireImage)
NEW YORK, NY - OCTOBER 03: Singers Olivia Newton-John and Melissa Etheridge visit the SiriusXM Studio on October 3, 2016 in New York City. (Photo by Cindy Ord/Getty Images)
LOS ANGELES, CA - MAY 21: Olivia Newton-John arrives for the Steve Irwin Gala Dinner at JW Marriott Los Angeles at L.A. LIVE on May 21, 2016 in Los Angeles, California. (Photo by Gabriel Olsen/FilmMagic)
LOS ANGELES, CA - MAY 21: Bindi Irwin (L) and Olivia Newton-John arrive for the Steve Irwin Gala Dinner at JW Marriott Los Angeles at L.A. LIVE on May 21, 2016 in Los Angeles, California. (Photo by Gabriel Olsen/FilmMagic)
ATLANTIC CITY, NJ - APRIL 22: Olivia Newton-John appears in concert in the Arena at Trump Taj Mahal on April 22, 2016 in Atlantic City, New Jersey. (Photo by Donald Kravitz/Getty Images)
LAS VEGAS, NV - JANUARY 23: Olivia Newton-John and Nevada Ballet Theatre's Future Dance students during Nevada Ballet Theater's 32nd Annual Black & White Ball honoring Olivia Newton-John at Wynn Las Vegas on January 23, 2016 in Las Vegas, Nevada. (Photo by Denise Truscello/WireImage)
LOS ANGELES, CALIFORNIA - APRIL 01: Singer Olivia Newton-John and her daughter Chloe Lattanzi on the red carpet for the Premiere of Syfy's 'Dead 7' at Harmony Gold on April 1, 2016 in Los Angeles, California. (Photo by Paul Redmond/WireImage)
LAS VEGAS, NV - JANUARY 23: Chippendsales dancers Ryan Stuart and James Davis pose for a photo with Leeza Gibbons (L) and Olivia Newton-John (2nd from R), at Nevada Ballet Theater's 32nd Annual Black & White Ball at Wynn Las Vegas on January 23, 2016 in Las Vegas, Nevada. (Photo by Denise Truscello/WireImage)
LAS VEGAS, NV - JANUARY 23: Entertainer Olivia Newton-John (R) and her husband, John Easterling, attend Nevada Ballet Theatre's 32nd annual Black & White Ball honoring her at Wynn Las Vegas on January 23, 2016 in Las Vegas, Nevada. (Photo by David Becker/Getty Images)
DANCING WITH THE STARS - 'Episode 2106' - The remaining nine celebrities returned to their original professional dance partners to tackle 'Famous Dances Night' on MONDAY, OCTOBER 19 (8:00-10:01 p.m., ET) on ABC's 'Dancing with the Stars.' Special guest Olivia Newton-John joined the judges' desk to see how the couples re-created iconic dance routines from movies and music videos. One couple was eliminated at the end of the night based on the lowest combined judges' scores and viewer's votes from the 'Switch Up' and 'Most Memorable Year' performances. (Photo by Adam Taylor/ABC via Getty Images) OLIVIA NEWTON-JOHN
LAS VEGAS, NV - AUGUST 09: Singer Chloe Lattanzi (L) and her mother, singer/actress Olivia Newton-John celebrate the 35th anniversary of 'Xanadu' with the world premiere of their music video 'You Have to Believe' at Share Nightclub on August 9, 2015 in Las Vegas, Nevada. (Photo by Bryan Steffy/WireImage)
LAS VEGAS, NV - AUGUST 09: (EXCLUSIVE COVERAGE) (L-R) John Easterling, and his wife, singer/actress Olivia Newton-John, daughter, singer Chloe Lattanzi and her fiance James Driskill attend the celebration of the 35th anniversary of 'Xanadu' with the world premiere of their music video 'You Have to Believe' at Share Nightclub on August 9, 2015 in Las Vegas, Nevada. (Photo by Bryan Steffy/WireImage)
LAS VEGAS, NV - MARCH 07: Entertainer Olivia Newton-John arrives at the 6th annual St. Baldrick's Foundation Head-Shaving Fundraiser at the New York-New York Hotel & Casino on March 7, 2015 in Las Vegas, Nevada. (Photo by Gabe Ginsberg/FilmMagic)
LAS VEGAS, NV - JANUARY 03: Entertainer Olivia Newton-John (L) and actress Didi Conn appear after they performed 'Summer Nights' together at Flamingo Las Vegas on January 3, 2015 in Las Vegas, Nevada. (Photo by David Becker/WireImage)
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The diagnosis comes 25 years after the former "Grease" star was diagnosed with breast cancer back in 1992. As E! News notes, she underwent a partial mastectomy, chemotherapy and breast reconstruction for her treatment back then.

"I decided on my direction of therapies after consultation with my doctors and natural therapists and the medical team at my Olivia Newton-John Cancer Wellness and Research Centre in Melbourne, Australia," Tuesday's statement continued, before noting that she wants to "focus on her treatment and healing."

The Olivia Newton-John Cancer Wellness and Research Centre was built back in 2008.

Read Olivia Newton-John's full Facebook post below:

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