Doctor Who fans watched the 50th anniversary episode in a worldwide simulcast.
The 75-minute episode, The Day of the Doctor, was broadcast in more than 90 countries at the same time as it was shown on BBC One.
It is also being screened in 3D in more than 1500 cinemas in Australia, Russia, Brazil, Mexico, Ecuador, Spain, Sweden, Norway and Iceland.
"It's the most ambitious episode we've ever done," said producer Steven Moffat.
The BBC reports it stars Matt Smith, David Tennant and John Hurt as different incarnations of the Doctor.
Jenna Coleman plays companion Clara and Billie Piper returns as Rose. Guest stars include Jemma Redgrave and Joanna Page as Elizabeth I in the 16th century.
The episode also features the Daleks and the return of the Zygons, shape-shifting aliens who first appeared in 1975.
The story is Smith's penultimate outing, before he regenerates at Christmas into a new Doctor, played by Peter Capaldi.
It began with Smith dangling from the Tardis as it flew over London.
According to the Guinness Book of World Records, Dr Who is the world's longest-running science fiction series.