Matt Smith said one saucy Doctor Who devotee nearly got more than they bargained for when his grandfather helped deal with his fan mail one day.
He told Graham Norton his mother normally dealt with the huge amount of mail he gets since being cast as the Time Lord.
Matt said: "Most of it is quite nice but my grandad helped one day and opened a letter that was rather suggestive and detailed what might happen if I visited the fan. He wrote back saying 'Matt can't make it, but I can'."
The actor, who is a guest on Norton's BBC One Christmas Eve show, said playing the part was "a privilege" but admitted it had taken its toll on his relationship with girlfriend Daisy Lowe.
He said: "She says it's not like having a boyfriend because I'm never there."
The Christmas Day episode shows Matt starring alongside singer Katherine Jenkins and Harry Potter star Michael Gambon in a story inspired by the classic Charles Dickens tale A Christmas Carol.