He was the man who made headlines when he died from heart failure after laughing non-stop at The Goodies.

Alex Mitchell's wife Nessie, who witnessed his death, even sent Tim Brooke-Taylor, Graeme Garden and Bill Oddie a letter thanking them for making her husband's final minutes so happy.

Now, 37 years on from the infamous 'Ecky-Thump' episode of the TV comedy, doctors think they know what caused the mysterious death of the King's Lynn man.

The clue came when Mr Mitchell's granddaughter Lisa Corke, 23, recently suffered a near-fatal cardiac arrest while relaxing at her home.

Doctors subsequently diagnosed her with Long QT syndrome, a rare form of heart disease which causes irregular heartbeats.

As the condition is hereditary, they believe Mr Mitchell, a bricklayer, must have also suffered from it and triggered a collapse with his laughing fit.

Mrs Corke, from the Isle of Sheppey, Kent, said: 'My granddad died from one of the most famous strange deaths.

'I think at the time they probably thought he suffered a heart attack caused by the laughter but doctors realised he died from a cardiac arrest caused by LQT syndrome after examining me.

'His death has been talked about for years and made all the papers at the time - I never knew him but it is strange to think we both had this life threatening condition.'

She now has a cardioverter-defibrillator in her chest, which detects arrhythmia and corrects it with a jolt of electricity, and will have to take medication for the rest of her life.

Alex, who was originally from Edinburgh died in front of his wife Nessie, who is now 86 and daughter Xia Mitchell, who is now 57.

He had two other children Liz Mitchell, 62 and Lisa's father Alex, 54.

Lisa's father Alex, who works as a mortgage consultant, said his father was a 'laid back' and 'cheerful man' who would have been happy to die laughing.

He said: 'He was a great man. He was always really cheerful and very laid back I think he found that particular sketch so funny because he was Scottish.

'It was hard for us to deal with at the time but we took comfort in the fact he passed away laughing. He would have been happy to go while laughing.

'It is amazing that after all these years we have finally found out what caused his death.'

The Goodies ran from 1970 to 1982. The 1975 Ecky-Thump episode – actually called Kung Fu Kapers – featured Brooke-Taylor as a kilted Scotsman who uses his bagpipes to defend himself against Oddie, a master of the ancient Lancastrian martial art of Ecky-Thump, which involves hitting people with black puddings.