Amie Henderson, 38, a friend and neighbour of the of the couple told the Daily Telegraph: "This is a very tight-knit expat community and we are all deeply shocked. There is anger too because every year there are hunting accidents."
Henderson, who runs a local magazine for holidaymakers called Morzine Source, added: "Marc had a lot of friends in the area. We'll all miss him."
Another local wrote on Facebook: "This is absolutely devastating. Everyone in our community will be affected by last night's accident. So very sad for Marc and everyone with him."
A source involved with the police investigation said: "He died instantly after being hit with a single bullet. The accident happened in thick woods. The shooter went into deep shock when he realised what he had done."
The source added: "He was riding a mountain bike on a popular and well used track, but it was difficult to get to and would not have been busy as darkness approached. The hunter may have mistaken him for an animal."
But a local prosecutor for the Thonon-Les-Bains region said: "Couldn't be confused with game, as he had a coloured helmet and a coloured mountain bike", suggesting the weapon might have gone off accidentally.
It is understood local police are treating the matter as aggravated manslaughter for which the gunman could be prosecuted and jailed.
It is the latest in a series of hunting accidents in which people have been killed or severely wounded.
Last year a 59-year-old hiker was shot dead by a hunter in the Drôme and a 13-year-old boy died when he was accidentally shot by his grandfather.
In 2017 a woman who had been sitting in her garden was killed after a stray hunter's bullet passeds through her garden hedge.
In 2016, there were 18 fatal hunting accidents reported in France.
