Millions of Doctor Who fans tuned in to last night's finale, the BBC has said, although there is still no confirmation David Tennant will return for the fifth series.
The penultimate episode saw the Time Lord, played by Tennant, shot by a Dalek and start to regenerate.
The scene caused fans to speculate Tennant was about to leave the series. Cast and crew were sworn to secrecy to keep last night's episode a surprise.
In the event, the Doctor did not regenerate, leaving the door open for Tennant to return. Next year there will be a series of one-off episodes, with a fifth series planned for 2010.
The BBC said it is too early to say whether Tennant will stay on for the next full series.
But in Saturday's episode, Catherine Tate, who plays the Doctor's companion Donna Noble, made her exit.
During the series finale, the doctor was cloned and Donna absorbed some of his mind, while the clone became half-human.
While the Doctor's clone left to live in a parallel universe with former companion Rose Tyler (Billie Piper), Donna had to have her mind wiped and she returned to her family, with no memory of her adventures.