The Gavin & Stacey star joined Time Lord actors Matt Smith and David Tennant and current companion Jenna-Louise Coleman at a read-through of the script on Monday (April 1).
The celebratory episode will also feature former Who star Billie Piper and veteran actor John Hurt.
The Steven Moffat-penned special begins filming this week, and is being shot in 3D. It will reportedly be 90 minutes long and receive a limited worldwide cinema release.
Smith claimed last month that the 50th anniversary is about honouring the show's past.
"It's about looking back and forward at the same time, a bit like the Doctor does," he explained.
"It's about celebrating everyone that's been involved with it, all the wonderful actors that have taken part before me, and it's also about looking forward."
In 2010, Page was forced to deny rumours that she had been cast in the BBC sci-fi, but admitted that she would love a role in the show.
"A friend was telling me about that. I was like, 'I wish it was true'," she said at the time.
"I think I've got to be the only Welsh actress who has never been in Doctor Who so if someone would like me to be in Doctor Who I would love the part."
She recently welcomed her first child with husband James Thornton, a daughter called Eva.
Watch the stars of Doctor Who talk the 50th anniversary special with Digital Spy below: