A motorcycle said to have featured in the 1969 road movie, Easy Rider, has been sold at auction for $1.35 million (£839,700) – despite claims that it may not be the real thing.

Questions over the authenticity of the customised Harley-Davidson were raised before the auction by another collector who claims that he owns the actual chopper used in the film.

Gordon Granger also claims that he has a certificate signed by actor Dan Haggerty, who had a small role in the classic movie and restored the bike, which proves that his is the real motorcycle ridden by Peter Fonda in the film.

However, Haggerty admitted to the Los Angeles Times he had authenticated and sold two “Captain America” bikes. Only one is thought to be the genuine article and that, Haggerty says, is the one sold on Saturday.

Peter Fonda, who also authenticated the machine, signing the teardrop-shaped gas tank, has expressed his dismay over the confusion. He told the Los Angeles Times that he wishes he had never lent his credibility to the motorcycle and wanted to warn potential bidders at the auction.

The makers of Easy Rider originally built four motorcycles – two “Captain America” bikes for Fonda’s character and two “Billy” bikes for his co-star Dennis Hopper’s – and only one is known to have survived.

But which one is it? It’s still not clear, and perhaps it never will be.

“There are only three possibilities,” Granger told the Los Angeles Times. “Either my bike is the real one, or the other one is the real one, or neither one is the real one.”