At its peak, the 75-minute episode, "The Day of the Doctor," drew 10.61 million viewers Sunday, with an overall average of 10.2 million viewers, the BBC reported Sunday.
The episode was aired concurrently in 94 countries, setting the Guinness World Record for "the world's largest ever simulcast of a TV drama."
"The Day of the Doctor" featured three Doctors: Matt Smith, the current Doctor; David Tennant, who portrayed the 10th doctor from 2005 to 2010; and John Hurt, who was recently introduced as the Doctor between Paul McGann's eighth Doctor and Chris Eccleston's ninth Doctor.
The three are brought together in the episode to determine the fate of Gallifrey, the planet from which the Doctor and all other Time Lords hail.
Billie Piper, who played the ninth and 10th Doctors' companion -- or sidekick -- Rose Tyler regularly from 2005-06, returned for the anniversary special, along with Jenna-Louise Coleman, who plays Clara Oswald, the Doctor's current companion.