Matt Smith's last episode as Doctor Who was re-written after he injured his leg, according to reports.
The injury was written into the script of the Christmas Day show so f ans will see the Time Lord lose a leg after a battle with the Weeping Angels.
The Sun reported that fans will see the doctor grow old fighting Cybermen and Daleks after being drawn back to a planet called Trenzalore by the sound of a bell.
Matt, who is replaced by Peter Capaldi in the Christmas Day episode, said he was excited about his final appearance.
Speaking last week, he said show boss Steven Moffat had given him a great exit.
He said: "I'm really excited about Christmas. I think Steven has written a real belter for me to go out on and I had a great time filming it.
"It was quite sad at the end, obviously, when I had to leave, but I think we've got a really moving story, a really great sense of adventure in it, which I'm pleased about because it's obviously the last episode but it still feels like a classic adventure episode with great monsters and a few twists."
Last week's 50th anniversary episode received a Guinness World Record for the world's largest simulcast of a TV drama.
The show set the record after being broadcast in 94 countries across six continents following a massive global campaign.
In addition to the TV broadcast, the episode was screened in more than 1,500 cinemas worldwide, including in the UK, US, Canada, Latin America, Germany, Russia and Scandinavia.
More than half a million tickets were sold for the theatrical screenings, at which fans were able to watch the episode in 3D.
A BBC spokeswoman said: "Doctor Who Christmas is a special moment for fans and while there's still huge amounts to be revealed, it is disappointing to see any spoilers, whether true or untrue, running in national press ahead of the episode."