She called him Fred. He called her Gladys. The world knew them as Charles and Camilla.

Now a new musical charts their 30-year love affair, which survived against all the odds, including the intervention of a certain princess.

The writers, Paul Tibbey and Mark Sims, saw the potential for a comedy in the curious behaviour of Prince Charles. Far from being charming, and sailing off into the sunset with his beautiful, young wife, he hankered after the woman who had set them up in the first place.

Tibbey, who also directs the show, says the joy of creating a royal comedy lay in imagining the behind the scenes relationship wrestling, including an encounter between Camilla and Diana, the rivals for Charles’ heart.

“It seemed to us that all the elements of the proper fairy tale romance were there – a love forbidden by the strict rules governing royal protocol, lovers stealing away for secret trysts, a golden coach taking the beautiful princess to her wedding in front of cheering crowds.

“As we said, all the elements are there... but, to quote the late lamented Mr Morecambe, not necessarily in the right order. And with an extra person thrown in to the mix – remember, there were three of them in this marriage.”

The show opens at Clapham’s Landor Theatre this week ahead of the forthcoming royal wedding between Charles and Diana’s eldest son, Prince William, and his fiancee Kate Middleton.

“The timing of it is quite fortuitous with the royal wedding,” adds Tibbey.

“This is one of the great love stories. It is not just about the love story itself but our relationship with the monarchy. Are they supposed to be people we look up to or are they just ordinary people? If so, why should we look up to them?

“It’s a comedy - but it also has some poignancy to it. It’s not a pantomime or a Spitting Image skit. But it is funny.

"You can’t have a singing Prince Charles, a singing Diana and Camilla on stage without some humour to it.”

Fred and Gladys, Landor Theatre, Landor Road, Clapham, until April 16, 7.30pm, £16, £14 concessions. Call 020 7737 7276, visit landortheatre.co.uk