Actress Jessica Chastain has been forced to ditch her plans to star in Iron Man 3 because of scheduling conflicts.

The Help star was set to play a scientist who develops a terrifying virus in the superhero sequel but she's apologised to her fans after turning down the role.

Chastain announced the news in a post on her Facebook.com page, writing: "Sorry to say that Iron Man 3 isn't going to work out. My schedule is jammed packed (sic) and I can't fit anything else in. The press announced my possible attachment far too soon. I know many of you wanted me to be involved, and I'm so sorry to disappoint you.

"Hopefully there'll be another Marvel film in my future. Shane Black and everyone on the IM3 team are really wonderful. I'm very excited to see the film when it comes out."

Iron Man 3 is due to be released next year.

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