The next series of Who Wants To Be A Millionaire? will see a UK contestant win the jackpot for the first time in 14 years.
The currently unnamed contestant answered all 15 questions correctly to become the show's sixth champion.
Host Jeremy Clarkson said he was "in awe" and believed them to be the best entrant in the programme's history.
This series was filmed without a studio audience, meaning the Ask The Audience lifeline has disappeared.
Instead, contestants have been able to use the Phone A Friend option twice. The new series of Who Wants To Be A Millionaire will begin on ITV next month.
'The best ever'
Clarkson said: "Well, I'm absolutely thrilled and delighted that we've found someone who seems to know just about everything.
"I can't wait for the viewers to see it and I want to watch it back too."
He continued: "I was just in awe of this contestant and think they are probably the best the show has ever had in its 22-year history.
"It was a joy to sit and watch it unfold."
Clarkson, who also hosts The Grand Tour, said the contestant "whizzed through the 15 questions and all of a sudden confetti was falling from the ceiling and I was saying, 'You've just won £1m'.
"I wasn't sure I'd ever get to utter those immortal six words and I'm not embarrassed to say, it was a little emotional but boy did it feel good."
But some were puzzled by the decision to announce the winner before the episode's broadcast, suggesting knowing in advance was a spoiler.
"I don't understand why ITV have told everyone that this has happened?" said TV critic Scott Bryan.
One fan replied: "Speaking as a regular viewer, this kind of ruins it for me. Part of the fun is the anticipation, and when you know it's going to happen, it's ruined."
But the Daily Mirror's showbiz editor Mark Jeffries tweeted: "My guess is 1) I think they thought it might leak 2) They are hoping it boosts ratings and people tune in every night for the whole run to make sure they see the winner."
In May, retired doctor Andrew Townsley, from Glasgow, came close to the jackpot but walked away with £500,000.
Ingram Wilcox was the most recent winner of the top prize, taking home £1m in 2006.
In all, five contestants have previously won the £1m prize on the UK version of Who Wants To Be A Millionaire?
That does not include Major Charles Ingram, who appeared to hit the jackpot but was later accused of cheating in the infamous coughing scandal. His story was recently depicted in the ITV drama Quiz.
The show's first millionaire was Judith Keppel in November 2000.
The other champions were David Edwards (2001), Robert Brydges (2001), Pat Gibson (2004) and Wilcox (2006).