The internet-only episode was announced yesterday when it emerged that Robert Sheehan, who played Nathan, will not be appearing in the third series.
The film, which is being written by Misfits creator Howard Overman, will deal with Nathan's departure and the arrival of new character Rudy.
The episode will see the group travel to Las Vegas, but the trip is said to end in "total disaster" for Nathan. Further details of his exit have not yet been released but E4 hinted that "it may or may not involve some pic 'n' mix, a Fisherman's Friend, and a Tripling incident".
Overman said: "It's great to be launching the third series of Misfits with an online film which introduces our new character Rudy, as well as saying goodbye to Nathan."
Meanwhile, Channel 4's drama commissioning editor Robert Wulff-Cochrane said: "We're all very excited about the return for a third series, as well as kicking off with a groundbreaking online film. Howard Overman has created some more brilliantly surprising and original storylines and fans can rest assured that series three will begin in a way no-one else could possibly imagine."
The online Misfits episode will be posted on the E4 website before the third series begins later this year.
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