Little Britain star David Walliams will attempt to swim the English Channel to raise money for Sport Relief.
The comedian, 34, hopes to complete the 21-mile charity swim in under 16 hours. A documentary covering his attempt will be shown on BBC One on 13 July.
Walliams has spent the last 11 months training with former Olympic pentathlete Greg Whyte.
"I reckon I have a 50/50 chance of getting across. I hope people see it as a symbolic thing," said Walliams.
"I'll just be in a pair of Speedos and goggles - it's what the public wants," he added.
Less than 10% of people who have attempted to swim the Channel have succeeded in reaching France.
"I've always loved swimming but I didn't really think how cold it would be and how far," said Walliams, who will have to contend with high winds and waves of up to two metres.
Mr Whyte praised the comedian's commitment.
"David has been working tirelessly over the past 11 months to make an attempt on the Channel, demonstrating a level of work and commitment as great as any elite athlete I have met," he said.
The former Olympic athlete described swimming the channel as "one of the toughest physical challenges on the planet".
The famous stretch of water is one of the world's busiest shipping lanes, with 600 tankers and 200 ferries crossing it every day.
Walliams will set off from Dover, Kent, and cover himself in grease to keep warm and food will be fed to him from a pole on his support boat during the swim.
The public can sponsor him on the Sport Relief Superswim website.
Organisers are asking members of the public to raise money themselves by running a mile on 15 July.
Sport Relief has raised £30m for charities in the UK and abroad since it launched in 2002.