The finale to the latest series of Doctor Who was seen by an average audience of 9.4m people on BBC One.
The final 15 minutes of the drama pulled in 9.8m viewers, capturing close to 50% of the entire TV audience.
After the Time Lord was wounded by a Dalek at the end of last week's episode, speculation had mounted that the Doctor would regenerate.
In a closely-guarded storyline, this failed to happen, leaving the way clear for actor David Tennant's return.
A fifth series of the show is scheduled for 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.
Tennant has been confirmed to star in the lead role for a number of BBC One specials next year.
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.