The Prince of Wales has recorded a message to be heard on a special Christmas Day episode.
In his message he talks about the show as "one of this country's great institutions" while trying to avoid a challenge from Paul Merton.
However he does not take part in a normal round of the game - his message will be played before the festive contest starts in earnest.
Host Nicholas Parsons said: "It was a pleasure to hear The Prince of Wales recount years of listening to Just a Minute with such fondness.
"But when he delivers his message will he make it to the end without hesitation, repetition or deviation? You'll find out on Christmas Day."
The radio quiz, in which contestants are challenged to speak for one minute without hesitation, deviation or repetition on any given subject, will turn 50 in December 2017.
Radio 4 controller Gwyneth Williams said it was "fitting" that the Prince of Wales should join the show as "we know the Prince of Wales has enjoyed BBC radio comedy over many years".
She added: "But Nicholas Parsons and Paul Merton take no hostages so I can only wish him luck!"
The Christmas special - titled Just a Minute Does Panto! - sees Merton, Gyles Brandreth and Sheila Hancock journey through Panto-land in search of the missing Golden Whistle, joined by Pippa Evans, Tony Hawks, Rufus Hound and Josie Lawrence.
It will be broadcast on BBC Radio 4 at 13:15 GMT on 25 December.
Prince Charles is to appear on BBC Radio 4's comedy quiz Just a Minute.