Ten Doctor Who actors from the past 50 years will say thank you to real doctors and other NHS staff on a star-studded BBC fundraising telethon later.
Jodie Whittaker will be joined by a host of her predecessors as the Doctor on BBC One’s The Big Night In.
Little Britain, Peter Kay, The Vicar of Dibley and Catherine Tate will all also return during the three-hour special.
The show begins at 19:00 BST and will see Children in Need and Comic Relief join forces for the first time.
The Doctors have recorded a message thanking front-line staff for their work during the coronavirus crisis. It will be broadcast just before the weekly Clap For Carers at 20:00 BST.
The actors taking part range from Tom Baker, who played the role between 1974-81, to current Tardis-dweller Jodie Whittaker, and Jo Martin, who appeared as an alternative incarnation of the Doctor in two episodes earlier this year.
Other highlights of the night will include Matt Lucas and David Walliams doing Little Britain on TV for the first time in a decade.
Dawn French will revive The Vicar of Dibley, and Kay will unveil a new video for (Is This The Way To) Amarillo.
Tate will bring back schoolgirl Lauren – who is struggling with being remotely educated by her teacher, played by David Tennant.
The three-hour show will aim to raise millions of pounds for vulnerable people around the UK who have been affected by the pandemic. The government has pledged to match all public donations, with a minimum of £20 million.
The programme also promises to “celebrate the acts of kindness, humour and the spirit of hope and resilience that is keeping the nation going”.
It will include the unveiling of a home-made video for a charity single featuring stars like Dua Lipa, Chris Martin and Rita Ora.
They – along with the likes of Ellie Goulding, Jess Glynne, Paloma Faith and Rag ‘N’ Bone Man – have recorded a cover of Foo Fighters’ 2003 track Times Like These.
Gary Barlow, Steve Coogan, Rob Brydon, Jack Whitehall, Romesh Ranganathan, Miranda Hart and the cast of People Just Do Nothing are among the others expected to appear on the show.
And the Strictly Come Dancing professionals have come up with a new routine for people to learn at home.
The programme will be hosted by Matt Baker, Zoe Ball, Sir Lenny Henry, Paddy McGuinness and Davina McCall.
“It’s so exciting to actually be able to do something positive… especially bringing Comic Relief and Children In Need together for one night only,” McCall told BBC Radio 5 Live on Wednesday.
“We’re actually going to be in a studio, which I’m personally extremely excited about – being in the same room as other people.
“We’re going to be in the BBC One Show studio, so there will be Matt, Lenny and me for the first hour and we will all be two metres apart.”
Sir Lenny told BBC Breakfast on Saturday: “We’re all going to be socially distanced, and then do a bit, and then move away from each other, and then nearly everybody else is doing stuff from home or from a remote location. It’s going to be great!”
The aim of the night is to let “the key workers and the care workers know that we really respect what they’re doing”, he said.
Speaking about the fundraising, he added: “A lot of the projects that we support have come to us and said that they’re really struggling in this time. They need our help.”
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