The actress, who is battling cancer for the third time, sat down for an interview with ET on Monday, where she revealed what she told the beloved Jeopardy! host after she learned of his diagnosis.
"I sent him a message saying, 'I know you can get through this,' and, 'Don't listen to stage four and all of [that],'" she explained. "'Don't read the statistics and stay focused and see how you can heal yourself.'"
"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."
As ET previously reported, Trebek revealed his diagnosis last Wednesday in a video shared to Jeopardy!'s YouTube page.
"Normally the prognosis for this is not very encouraging, but I'm going to fight this, and I'm going to keep working," Trebek, 78, exclaimed. "And with the love and support from my family and friends, and with the help of your prayers also, I plan to beat the low survival rates statistics for this disease."
"Truth be told I have to, because under the terms of my contract I have to host Jeopardy! for three more years," he joked. "So, help me keep the faith, and we'll win. We'll get it done. Thank you."
Newton-John revealed last September during the Australian news program Sunday Night that she was in recovery again for cancer after doctors discovered a tumor at the base of her spine.
"I'm one of millions in this fight, in this journey," she said at the time. "A lot of people see it as a fight and wherever you choose to see it, that’s your prerogative. ... I see it as part of my mission, maybe."
"There are other people out there doing much, much worse than me," she added. "And I'm very a privileged person and I'm very aware of that. I have nothing to really complain about."
The Grease star was first diagnosed with breast cancer in 1992. She beat the disease after months of chemotherapy treatments and a partial mastectomy but revealed in May 2017 that the breast cancer had returned, spreading to her shoulder.
For more from our exclusive interview with Newton-John, tune into Entertainment Tonight on Monday, and pick up her memoir, Don't Stop Believin', out Tuesday.