Beloved game-show host Alex Trebek announced he's been diagnosed with advanced pancreatic cancer in a YouTube video on Wednesday that had a positive tone despite the grim prognosis.

"Just like 50,000 other people in the United States each year, this week I was diagnosed with Stage 4 pancreatic cancer," Trebek said in the message posted on the Jeopardy YouTube channel.

"Now, normally the prognosis for this is not very encouraging. But, I'm going to fight this and I'm going to keep working. And with the love and support of my family and friends, and with the help of your prayers also, I plan to beat the low survival rate statistics for this disease.

"Truth told — I have to, because under the terms of my contract, I have to host Jeopardy for three more years," the 78-year-old continued, wearing a signature suit on the Jeopardy set and employing the wry wit he has brought to the hit quiz show for decades.

A Message from Alex Trebek: <a href="https://t.co/LbxcIyeTCF">pic.twitter.com/LbxcIyeTCF</a> —@Jeopardy

"So help me: keep the faith and we'll win. We'll get it done. Thank you."

Born in Sudbury, Ont., Trebek attended the University of Ottawa and hosted a number of CBC TV programs early in his career, including the high school quiz show Reach for the Top.

He moved to the United States in the 1970s and became a U.S. citizen in 1998. He and his wife, Jean Currivan, have two children.

Trebek has won several Emmy Awards for hosting Jeopardy since 1984. His matter-of-fact delivery style and genial personality have made him a worldwide star and the subject of spoofs on Saturday Night Live.

An officer of the Order of Canada

Trebek became an officer of the Order of Canada in 2017 in recognition of his "iconic television work" and commitment to educational, environmental and humanitarian causes.

In late 2017, Jeopardy went on hiatus after Trebek underwent surgery for blood clots on his brain caused by a fall.

Several months after the surgery, he appeared in a video on the show's Facebook page, wearing a Jeopardy baseball cap.

Using the same tone he employs to explain difficult subjects on the show, the unflappable Trebek said: "I had a slight medical problem, subdural hematoma, blood clots on the brain caused by a fall I endured about two months ago."

In 2007, he was hospitalized for about a week after suffering what was described as a minor heart attack.

Sharing his cancer diagnosis was "in keeping with my longtime policy of being open and transparent with our Jeopardy fan base," Trebek said.

"I also wanted to prevent you from reading or hearing some overblown or inaccurate reports regarding my health. So therefore, I wanted to be the one to pass along this information."

Social media flooded with tributes

Keep fighting, Alex – Canadians are rooting for you! <a href="https://t.co/EY3Tm1uKVx">https://t.co/EY3Tm1uKVx</a> —@JustinTrudeau Social media was flooded with tributes for Trebek after his announcement.

Former Ontario premier Bob Rae shared his sympathies on Twitter, calling Trebek a "very fine man."

Ken Jennings, who holds the record for the longest winning streak on Jeopardy, tweeted that he hopes Trebek finds comfort in the millions of fans who are rooting for him, warning, "I hope some very good L.A. oncologists are getting ready to have their mispronunciations corrected."

I’ve said this before but Alex Trebek is in a way the last Cronkite: authoritative, reassuring TV voice you hear every night, almost to the point of ritual. —@KenJennings

Singer-songwriter Ron Sexsmith also sent his positive thoughts to the "great Canadian" via social media.

The Sajak family is deeply saddened to hear of Alex Trebek’s struggle with cancer. Our hearts go out to him and his family. But there is no one I know who is stronger and more determined, and I would never bet against him. We, and the entire country, are pulling for you, Alex. —@patsajak The show has yet to bring in a substitute host— save once, when Trebek and Wheel of Fortune host Pat Sajak swapped their TV jobs as an April Fools' Day prank.

Trebek, the smoothest of TV game show hosts, admitted to a case of nerves during rehearsals in January for the show's first All-Star Games, a team-play tournament that made new demands on its host.

"This will probably start me drinking again," he joked.

The clue: “He has the strength and determination to beat his cancer diagnosis.” The response: “Who is Alex Trebek?” My family and I are sending love and tons of healing prayers to you Alex. <a href="https://t.co/VTA435hHel">pic.twitter.com/VTA435hHel</a> —@TheVannaWhite Although Trebek had publicly toyed with the idea of retiring, he instead renewed his deal in 2018 with Sony Pictures Television for three more years, through the 2021-22 season.

In a January interview with The Associated Press, Trebek discussed his decision to keep going with Jeopardy.

"It's not as if I'm overworked -- we tape 46 days a year," he said. But he noted he's been working in TV for more than 50 years and was "78-and-a-half now. I'm slowing down."

"It's logical to start thinking about retiring," he said. "And I will someday, when I feel I've lost enough of my abilities and am messing up a little too much, or it's no longer any fun."

"And it's still fun," he said.