Red Nose Day Actually will be written by Richard Curtis and star Hugh Grant, Keira Knightley and Colin Firth.
Liam Neeson, Bill Nighy and Rowan Atkinson will also appear in the film, which sets out to discover what the original characters are doing in 2017.
The 10-minute sequel will be shown on 24 March on BBC One as part of the Red Nose Day appeal.
Many have suggested a tribute to the late Alan Rickman, who starred in the original.
Another suggestion tweeted to Freud involved Atkinson’s character, who was seen in the original as a shop assistant