Comedians French and Saunders are doing a send-up of the second movie, called Harry Potter and the Secret Chamber Pot of Azerbaijan.
Dawn French is going to play the boy wizard and Jennifer Saunders will be Hermione.
Basil Brush is Dobby
Posh British actor Jeremy Irons will play Snape, and tiny comedian Ronnie Corbett is taking on the part of giant Hagrid.
Bottom star Adrian Edmondson, who's married to Jennifer Saunders, is directing the sketch.
"What great casting," he said. "Meeting Basil was a high point of my career. He is a genuine person."
Potter author JK Rowling was at the launch of Comic Relief and posed with a red nose with comedian Lenny Henry.
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I met the stars at the Comic Relief launch
