Olivia Newton-John on Going ‘Undercover’ While Learning to Walk Again Amid Cancer Battle (Exclusive)

The 'Grease' icon shared what she did to hide her identity while fighting cancer at her hospital in Australia.

Olivia Newton-John revealed she donned a beanie and masks to conceal her identity while in the hospital recovering from her third battle against cancer.

The 70-year-old Grease star was admitted to her own facility, the Olivia Newton-John Cancer Wellness & Research Center in Australia in 2018, after her cancer returned in the form of a tumor in her lower spine.

“Nobody knew I was there, so I was undercover boss in the hospital -- on purpose,” she said in a sit-down interview with ET’s Nancy O’Dell to promote her new memoir, Don't Stop Believin'. “I didn’t want people to know because I didn’t want it to be out there in the public that I was in the hospital.”

“I was learning how to walk again,” Newton-John continued. “I was using a walker, so I’d wear a beanie and glasses and masks, so no one would know who I was.”

Newton-John was first diagnosed with breast cancer in 1992. It later returned, then came back again as a tumor in her lower spine, which caused a fractured pelvis -- and subsequently, the intense pain she suffered while participating in a 2018 charity walk for breast cancer.

Following the walk, she wound up in the hospital. Today, she has completed radiotherapy, is on an oral hormonal therapy involving “tons” of herbs and vitamins, and is feeling "great."

She has also been using cannabis, which has significantly helped her through the health battle.

“Cannabis has been incredible for me for pain and for sleep and for anxiety,” she shared. “It’s an incredible plant that is helping so many people with different issues.”

Despite the struggles, Newton-John has admirably maintained a positive attitude and says she sees every day as a “gift.”

“Every day’s a gift anyway,” she said. “We don’t really know how long our life is, so every day is an extra bonus for me and I’m very grateful and I intend to be here for a long time. I have much to do, still, and I’m enjoying my life.”

During ET’s chat with Newton-John, the Aussie icon also shared what advice she gave to Jeopardy! host, Alex Trebek, following his recent stage four pancreatic cancer announcement.

"I sent him a message saying, 'I know you can get through this,' and, 'Don't listen to stage four and all of [that]. Don't read the statistics and stay focused and see how you can heal yourself,’” she said.

"That helps. Sense of humor is vital," she added. "He has a great attitude and a great sense of humor about it and I'm sure he'll do very well."

For more from our interview with Newton-John, tune into Entertainment Tonight on Monday, and pick up her memoir, Don't Stop Believin', out Tuesday.