The TV presenting duo have been friends for almost 30 years but have never celebrated Christmas together.
The TV hosts have swapped early morning starts in the Australian jungle for night shoots in the spooky Welsh castle – heading home after midnight.
Hosts Ant and Dec will be tested every three days and must wear 'proximity buzzers' reminding them not to get too close to others.
The show has been moved from New South Wales, Australia, to a castle in North Wales, UK.
The SM:TV gang have shared a sneak peek of their reunion, 18 years on from the ITV morning show's final show.
Audience members Rob and Annette were challenged to snog live on the ITV show in a bid to embarrass their children and win a trip to