Peter Davison and Bernard Cribbins are among the special guests who will appear on Doctor Who Live: The Next Doctor tonight (August 4).
The identity of the 12th Doctor will be revealed on the show, with host Zoe Ball interviewing the new Time Lord.
Davison and Cribbins - who played the Fifth Doctor and Wilfred Mott respectively - will be joined in the studio by Outnumbered's Daniel Roche, Rufus Hound and Liza Tarbuck.
Head writer Steven Moffat and current Doctor Matt Smith will also be on hand to speak to Ball about the show's newest star.
There will be special video messages from former Doctor Tom Baker, writer Mark Gatiss and Radio 1's Jo Whiley.
Bruno Tonioli, Katy Manning, Anneke Wills, Janet Fielding and Bonnie Langford have also pre-recorded special messages.
Could it be Peter Capaldi? Or even Hugh Grant? As the BBC prepares to unveil the new star of Doctor Who on live television for the first time, the nation is still in the dark over the latest incarnation of its favourite Time Lord. Which is just how the broadcaster wanted it.
No one could accuse the corporation of failing to milk the regeneration moment. As the 50th anniversary of the first episode approaches, an extravagant celebration will be broadcast on 4 August , climaxing with the naming of the 12th actor to play the Doctor. The special 30-minute programme, in a coveted 7pm slot, was parachuted into the sedate BBC1 Sunday night schedule late last week of Countryfile and Antiques Roadshow, the outcome of some cloak-and-dagger planning. The project even had its own codename: Houdini.
It was put together at speed over the past month by a small group of entertainment producers. Charlotte Moore, the new controller of BBC1, who has school-age children, hit on the idea of a live event after being appointed in June.
The guest list of former Doctor Who stars and celebrity fans who will be in the 400-strong audience at the BBC studio complex in Elstree was still being compiled as the deadline approached. A battalion of Daleks – who will also have a starring role in the 23 November Doctor Who special – are expected to be present, alongside the much-loved fourth Doctor Tom Baker and Billie Piper, who played Rose Tyler in the 2005 revival of the series. Lead writer and executive producer Steven Moffat describes playing the Doctor as one of "the biggest roles in British television".
While bookmakers are busily marking up the odds and raking in the bets – with Peter Capaldi, who played the foul-mouthed Malcom Tucker in The Thick of It the clear favourite – Moffat's mother-in-law, veteran producer Beryl Vertue, said she had no privileged access to the crucial information: "I have no idea who it is," she told the Observer. "I really don't. I always say to Steven, 'don't tell me', and he doesn't. But I think it is lovely that this is happening, that there is such excitement over this programme after 50 years. It just shows you the power it has."
Russell T Davies, the Doctor Who fan and producer who revived the show against the odds in 2005, will not be in attendance. Davies expanded the brand with spin-offs including Torchwood and The Sarah Jane Adventures before handing creative control to Moffat three years ago. He told the Observer: "I'm trying to keep my head down. I feel like a ghost at the feast. I will be watching from home."
Since its revival, Doctor Who has become one of the top five BBC "superbrands" – another is Top Gear – selling to about 50 countries. But after winning a UK audience of 10.8 million in 2005, it is now thought to need refreshment – and some less impenetrable plots.
Moffat will appear live tonight, as will outgoing Doctor Matt Smith, and the show will be hosted by Zoe Ball. BBC Wales will start filming the next series in October.
There have been calls for the Doctor to be played by a black actor, such as Idris Elba (who has ruled himself out), a woman (Sheridan Smith) or an older figure (Hugh Grant), but David Tennant and Smith appear to have established a trend for younger actors on the cusp of breakthrough who have good comic timing. Doctor Who regenerates on its own terms, though, and is increasingly wooing US fans. So who knows?
Only a short 16 hours to go, ONTD. Dibs on the party post.
ETA: The official Doctor Who page is inviting fans to submit questions for the 12th Doctor once he
"Why aren't you a woman?" has already been taken by me.