Olivia Newton-John thought her ex-boyfriend, Patrick McDermott, was either “killed” or “drowned” when he went missing off the coast of Los Angeles 21 years ago.

Matthew Hild covers the cameraman’s mysterious 2005 disappearance in his new biography on the late “Grease” star, “A Little More Love: The Life and Legacy of Olivia Newton-John,” which comes out Thursday.

The writer interviewed many of Newton-John’s friends and colleagues for the book, and one told Hild what the four-time Grammy winner really believed happened to her “on-again, off-again” partner.

“She thought he’d been killed,” Newton-John’s friend and collaborator Liona Boyd told Hild, per People. “She thought he drowned.”

Boyd added, “She didn’t believe all the rumors about the sightings in Mexico. She said, ‘No, I don’t believe that.'”

Newton-John began dating McDermott shortly after her divorce from her first husband, actor Matt Lattanzi, in 1995.

The “Two of a Kind” star described the pair’s relationship as “on-again, off-again” in her 2018 memoir and revealed she and McDermott were “off-again” at the time of his disappearance during an overnight fishing trip in June 2005.

Rumors began to swirl about what may have really happened to the 48-year-old McDermott, including speculation that he “staged his disappearance” and ran away to Mexico amid money problems.

“Whether he had financial difficulties and staged his disappearance, whether it was a murder or an abduction, no one seems to know,” Louise Pennell, a foreign correspondent for Seven Network Australia, told NBC News in 2005.

“What we do know is that there were some problems with finances. Patrick McDermott, on the fishing boat, told the crew that he had some alimony troubles with his ex-wife, who is an actress,” Pennell added. “As far as I know, he complained about financial troubles with her.”

McDermott had divorced actress Yvette Nipar in June 1993. The former couple shared one child, a son named Chance.

Another person, investigator John Nazarian, claimed he saw the missing photographer with a woman in Mexico after he was reported missing.

“I spoke to people there,” Nazarian said in 2016. “The girl he was traveling with was described as having a German accent.”

But according to Hild’s upcoming book, Newton-John approached a security expert named Gavin de Becker, who sent private investigators down to Mexico in search of her missing ex to no avail.

The US Coast Guard concluded McDermott was likely “lost at sea” following investigations that ended in 2008.

Newton-John publicly addressed her ex’s disappearance for the first time one year after the Coast Guard’s findings were released.

“I think there will always be a question mark … I don’t think I will ever really be at peace with it,” she told the Australian outlet Women’s Weekly in 2009.

The “I Honestly Love You” singer addressed McDermott’s disappearance further during an interview with Australia’s “60 Minutes” in 2016.

“He was lost at sea, and nobody really knows what happened,” she shared.

“It’s human to wonder. But you know, those are the things in life you have to accept and let go,” Newton-John continued. “Because whenever you go through difficult times, there are always those concerns.”

The Australian icon ultimately moved on and married her third husband, businessman John Easterling, in 2008 amid the mystery of McDermott’s disappearance.

Newton-John and Easterling were still married when she died in August 2022 at the age of 73 following a 30-year battle with breast cancer.