The "Let's Get Physical" songbird and Grease star revealed the news in an emotional interview with Channel 7's Sunday Night and has vowed that she will continue to work to help other cancer victims.
The channel teased their interview with Newton-John, 69, as a major "health announcement."
It was billed as "the interview Olivia Newton-John knew she had to do," adding that this interview would allow her to set "the record straight while she can."
Newton-John said in the clip for the show set to air Sunday night, "I wasn't sure, you know if I'd make it."
She revealed that she'd secretly battled a second bout of breast cancer back in 2013.
The superstar, who is currently fighting the disease for a third time, explained why she chose not to go public with the 2013 diagnosis at the time.
She told the program: "I thought 'It's my life' and I just decided to keep it to myself.'"
The star said in 2013, she was involved in a minor car accident, and a lump appeared in her right shoulder.
Scans revealed it was the return of the breast cancer she had beaten two decades earlier.
In 1992, Newton-John had undergone a partial mastectomy for a tumor in her breast when she was just 43 years old.
In May 2017, Newton-John announced that breast cancer had come back and had "metastasized to the sacrum."
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RadarOnline.com exclusively reported just weeks ago that her cancer has returned with a vengeance — as the killer disease had spread into the bones of her lower back.
Newton-John had cancelled some personal appearances, but told the media last month she was doing fine.
However, a source told RadarOnline.com, "This is her final fight and she promises to go out swinging.
"At this point, her goal is to make it to her 70th birthday on Sept. 26th and have a big celebration."
Newton-John, who has one daughter, Chloe, is a fighter. She has bravely said in the past that she's a "cancer thriver, not a cancer survivor."
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