Channel 4 has commissioned a new show which will see celebrities train to walk a 1000ft-length high wire suspended 300ft up in the London sky.
Don't Look Down - being staged in aid of Stand Up To Cancer - is hosted by Paddy McGuinness and will follow the group of famous faces as they attend a summer training camp in the Austrian Alps.
The series will culminate with the celebs - including McGuinness himself - performing the terrifying relay walk above some of the capital's most iconic landmarks.
"I've done all kinds of shows, but this is definitely the most nerve racking!" McGuinness said.
"I'm so excited to be hosting Don't Look Down, which is undoubtedly going to be the challenge of a lifetime for everyone involved. I can't wait to get cracking and see whether I can lead the team to find the nerve to take on this ridiculously high and very difficult walk.
"They're not going to be in for an easy ride, but it's all for such a brilliant cause and I hope we raise loads of money for Stand Up To Cancer. I'm now off to practice on the washing line."
C4 entertainment head Phil Harris added: "Don't Look Down is following in Channel 4's tradition of boundary-pushing reality formats. It's going to deliver everything from nerves and tears to laughs and camaraderie, cumulating in the most audacious of final stunts.
"We're thrilled to be working with Paddy again as he hosts the series and leads our celebs in their sky-high challenge, all part of a hugely ambitious year of Stand Up To Cancer. This is event television not to be missed."
The five-episode series is expected to air later this year.
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