Cast members from Back to the Future have sparked excitement by reuniting at a fan event, 33 years after making the first film in the trilogy.

Christopher Lloyd, who played the eccentric time-travelling scientist Doc Brown in the sci-fi series, posted a photo to Instagram where he posed alongside his former castmates Michael J. Fox, aka Marty McFly, Lea Thompson who played Marty's mum, and Thomas Wilson, who played the main antagonist in movies.

Lloyd captioned the photo: "This was special."

The actors were attending the Fan Expo Boston convention when they posed for the picture.

Thompson posted the same photo with the caption: "Four old friends get back from the future", while Wilson wrote: "Wow. This just happened."

The cast took part in a panel discussion at the fan event where they addressed speculation that a fourth film could be on the cards.

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Wilson reportedly joked of a potential reboot: "Basically, I think America is saying, 'Come on they've wrecked every other franchise with bad sequels, why not this one? C'mon, we would watch it until it sucks'."

However, Fox, who was diagnosed with Parkinson's disease in 1991, added that the actors have no say in whether another movie gets made, saying that co-creator Bob Gale is the "gatekeeper of the franchise".

Producer and co-writer Gale has previously indicated he has no interest in reactivating the series, saying: "We don’t need the money!"

Meanwhile, director Robert Zemeckis insisted that he will never agree to a remake, stating: "That can't happen until both [co-writer Bob Gale] and I are dead."

Back To The Future was released in 1985 and sequels followed in 1989 and 1990.