Chris Tarrant will be quizzing former Got Talent finalists including Paul Potts and Stavros Flatley in the famous hot seat.
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© ITV
Other reality TV stars taking part include teenage singer Shaheen Jafargholi and dance duo Twist & Pulse.
"We're well practiced as a team and we've been writing questions for each other in preparation. We've very high hopes of hitting the million!" said Twist Pulse.
Stavros Flatley's Demetrios Demetriou said: "We're very lucky to be in the position to take part in the show and help a great cause, I just need to become more decisive as I'm terrible at making decisions. Lagi will no doubt keep me in check."
Who Wants to Be a Millionaire: Britain's Got Talent Special airs on Sunday, May 6 on ITV1.
