David Tennant said that viewers would be left heartbroken by the final "brilliant" plot twists as he bows out of Doctor Who.
Tennant, 38, who has been hailed by many as the best Doctor in the Time Lord's history, gave a hint about the big climax to the epic tale, which airs on BBC1 on New Year's Day.
The story, titled The End of Time, Part Two, sees the 10th Doctor facing the end of his life as the prophecy "He will knock four times" looms, while the terrifying plans of his nemesis the Master spin out of control.
Tennant told BBC Breakfast: "Coming to the final episodes, you (think) will these live up to one's hopes for what that finale will be?
"And then you read the script - The Doctor's been told he's going to die, he knows he's going to die, so you get to play that new flavour with this character that you've got to know so well... suddenly you're playing a man who knows his end is coming.
"He's been told: 'He will knock four times' and you get the Master with these four beats in his head and you think, well, that's what that is. When you find out tomorrow night what that really means - (it) just breaks your heart - it's brilliant."
He confessed to being "maybe a little" jealous of new Doctor Matt Smith because of the fantastic time he would be having in the job.
Tennant, who has filmed a pilot for a show in the United States called Rex Is Not Your Lawyer, was asked about his plans for the future. He said: "I'm sort of waiting to hear, to be honest with you... it could go one of two ways and I'm literally waiting to be told."
Asked what he would be doing if he had not taken the Doctor Who job, Tennant told BBC1: "Who knows? It's like Sliding Doors isn't it? Things can work out very differently... even when I accepted it I had no conception that four years later it would still be going strong."
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In another interview, Tennant was also asked about speculation that Madonna had approached him to take part in a movie project. But he told GMTV: "I've never met the woman. She's never called me."
