Millions of Doctor Who fans have tuned in for the finale of the current series after last week's episode ended with the Doctor being shot by a Dalek.
With the Time Lord apparently starting the process of regeneration, there had been speculation Saturday's show could be the last for star David Tennant.
Cast and crew had been sworn to secrecy so the storyline was kept confidential.
In the end he did not regenerate, leaving the way open for Tennant to return for a fifth series in 2010.
In Saturday's episode the Doctor was helped by a small army of his companions to once again defeat the Daleks and their evil creator Davros to save the universe.
In an episode packed with unexpected twists, the Doctor was cloned and current companion Catherine Tate's character Donna Noble absorbed some of his mind to become half-Time Lord.
At the end of the episode the Doctor left his cloned self - who was half-human and as such will age and die - to live with his former companion Rose Tyler, played by Billie Piper, in another reality.
The producer of Doctor Who Confidential explains the 'regeneration' in the finale
The Doctor also separated from Donna, who had to have her mind wiped of all memories of their time together, before departing on his own in the Tardis.
In the run-up to Saturday's show, Freema Agyeman, who played the Doctor's last companion but one, Martha Jones, said the outcome was "the secret of all secrets".
About 7.4 million people tuned in for last week's episode and Agyeman said she had had "lots of texts and people coming up to me in the street asking if David is leaving".
Tennant has been confirmed to star in the lead role for a number of BBC One specials next year but those behind the show have been saying it is too early to confirm whether he will be in the next full series.
The fifth series, with Bafta-winning writer Steven Moffat at the helm, is scheduled to be broadcast on BBC One early the following year.
Moffat is to take over from current writer and executive producer, Russell T Davies, from 2010.
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