BAFTA-winning actress Daisy May Cooper and brother Charlie will join the line-up on Celebrity Traitors as a pair.
The siblings have been signed up as BBC bosses were keen to have a duo on the murder mystery show.
Daisy, 38, and Charlie, 35, creators of award-winning comedy This Country, stepped in after retired tennis ace Sir Andy Murray and mum Judy turned down the chance to join Claudia Winkleman’s show.
Mum and son Diane and Ross Carson were standout characters in the second civilian series.
This will be the first celebrity version of Traitors — where Faithfuls have to guess who is lying to win a cash prize.
A source said: “Bosses are convinced Daisy and Charlie will be great players.
“They’re hilarious, witty and have award-winning acting skills.”
The Coopers are expected to join Clare Balding, Tom Daley, Stephen Fry and Robert Peston with filming to begin next year.
A Traitors spokesperson said: “This is a game of lies so it would be foolhardy for Faithfuls to speculate before it begins.”
Daisy also appears on Never Mind The Buzzcocks.
She and Charlie, 35, shot to fame in 2014 when they co-wrote and starred in This Country, a sitcom based on their lives in the Cotswolds.
