First up tonight are presenter Johnny Vaughan, ex-cricketer Michael Vaughan, Harry Potter star Bonnie Wright and Downton actress Samantha Bond.
Sue Perkins is going solo without Mel to present, but she'll be joined by guest hosts Omid Djalili, Ed Byrne and Jo Brand.
Others taking part later in the week are Michael Ball, Emma Freud, Jason Gardiner, Jane Horrocks, Rochelle Humes, Jamelia, Doon Mackichan, Alistair McGowan, Victoria Pendleton, Greg Rutherford, Helen Skelton and Kirsty Young.
Who'll impress with their pies and puds? And who'll hang their heads in shame at their soggy bottoms?
The Great Sport Relief Bake Off, BBC2, 8.30pm
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