Peter Davison will play the ghost of William IV, who Wills (Hugh Skinner) consults about his famously small coronation.
Peter will join returning cast Charles (Harry Enfield), Camilla (Haydn Gwynne), Wills (Hugh Skinner), Kate (Louise Ford), Harry (Richard Goulding), Meghan (Kathryn Drysdale), Pippa Middleton (Morgana Robinson), Beatrice (Ellie White), Eugenie (Celeste Dring), Anne (Vicki Pepperdine) and Edward (Matthew Cottle).
Peter Davison said: I am a huge fan of the show, and I'm very pleased to be asked to appear in the Coronation Special, even if I am only an apparition. After many years going from playing vets, to doctors, to policemen, to vicars, and then barristers, I can see I've now reached the 'ghost' phase of my career - this is not necessarily a good sign, but it was a joy to do it.
The Windsors Coronation Special airs Sunday at 9pm on Channel 4.