Geordie duo Ant and Dec are so in tune they accidentally bought each other identical Christmas presents.
Donnelly said: " I remember seeing it and thinking Ant would like that and I would like one myself.
"And we ended up buying it for each other. We did laugh a lot when we realised."
The show, which raises money for charities including Barnardo's and the British Heart Foundation, is broadcast on Friday December 20.
It will include Pogues frontman Shane MacGowan teaming up with the cast of Coronation Street for a song and a special version of dating show Take Me Out for the over-50s.
Donnelly said presenting the show can be tough, adding: " When you hear some of the stories, they really do make your heart ache.
"I do well up. Most of us are having a really good time with family and friends at Christmas but not everyone is as lucky and so it is a really nice thing to be able to help people at that time of year."