Fred Sirieix "vomited everywhere" after the first day of rehearsals for the Strictly Come Dancing Christmas special.
The First Dates star is being partnered by Dianne Buswell on the festive special of the BBC One show - which airs on Christmas Day - and he revealed the tough training left him with bleeding feet and feeling nauseous.
Explaining how hard the rehearsals were for him, Fred revealed how he lost three kilos in just three weeks as Dianne put him through his paces in preparation for the show, where he will dance a quickstep to Merry Christmas Everyone by Shakin' Stevens.
Speaking to hosts Dermot O'Leary and Alison Hammond on This Morning, he said: "We trained for four hours. My feet were bleeding. I went back home and I was vomiting everywhere.
"My body couldn't take it. I lost three kilos in three weeks of training. Now I'm back to my fighting weight."
Fred considers himself to be quite confident - but says it was a whole different thing on the Strictly dancefloor.
"Well I got a call about four weeks ago now and they said, did you want to take part in the Strictly Christmas special and I got so scared. So scared because I can't dance," he added.
"And then the other thing is about confidence because I'm a confident guy, I'm not shy but although I'm confident, I was thinking am I going to be able to be confident and also pull it off on the day."
He continued: "I wanted to just dance and enjoy the experience or am I going to freeze and make silly mistakes?"
Last month, Fred was confirmed for the BBC One show, where he will compete against Anne-Marie, Adrian Chiles, Moira Stewart as well as The Repair Shop's Jay Blades and presenter Mel Giedroyc.
"I absolutely love Christmas so I’m delighted to be taking part in the Strictly Christmas special and to be partnered with the magnificent Dianne," Fred said in a statement.
"I hope my dance moves bring some Christmas joy to everybody watching at home and don’t make the judges say 'Bah, Humbug!' I got the phone call and I was as excited as I was scared."
He added: "Because I was so scared I thought I have got to do it. There is no way I can turn this down. I have got to do it."
