A Chinese cinema has accidentally advertised superhero sequel Thor: The Dark World with a photoshopped poster in which rival comic book titans Thor and Loki appear to be cuddling.

The manipulated image, originally created by a Weibo user known online as bbqfish2012, turned up at a Shanghai multiplex showing the Marvel comic book caper. It shows Thor protectively embracing his mischievous sibling, as Loki nuzzles into the Asgardian princeling's blond mane.

bbqfish2012 herself has reportedly since commented: "Damn it! If I were paid 1 yuan each time the photo is retweeted, I would be rich."

The image, compiled from separate shots of Chris Hemsworth's Thor embracing his human belle Jane Foster (Natalie Portman) and Tom Hiddleston's Loki standing alone, plays on the bromantic relationship between the pair in the comic book sequel. Thor: The Dark World sees the estranged brothers forced to team up to take on an even greater threat, Christopher Eccleston's nefarious Malekith.

Alan Taylor's film hammered its way to a mighty $109.4m (£68.3m) worldwide on debut at the weekend, despite not yet having opened in any of the world's three largest countries in terms of box office clout, the US, China and Japan. It is the sequel to 2011's Thor, and also continues the story from last year's box office megalith The Avengers.

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• Guardian review, Observer review, first look review