'It' author Stephen King was terrified by the changes made to the latest adaptation of his classic novel.

The iconic horror writer didn't have huge involvement in the writing of the big screen take on his 1986 book, but producer Barbara Muschietti has revealed he certainly approved of new 'scares' she and her brother - director Alex - put into the movie.

Referring to a scene in which one of the young children was terrorised by a woman from an old painting, she told Collider: ''Stephen King, the first email he sent to Andy when he had seen the movie, the one fear he wrote back, he said, 'I f***ing love the woman in the painting, it scared the s**t out of me.' ''

The fearful moment wasn't in the novel - nor was it included in the 1990 mini-series starring Tim Curry as Pennywise - but the siblings took influence from their own lives to give the film their own twist.

Barbara added: ''For instance, our mom had a print of a Modigliani painting at home and actually, there's a bit of a precedence in Mama there; Mama looks very Modigliani-esque.

''It was something that terrified Andy always, that print, and here you see it in the form of Judith. Judith is that fear for Andy.

''And then, the hair, for instance, with Beverly, that was actually a combined [effort] ... I collaborated there because I felt very attached to her hair and when she cut it, I felt that her hair should come back for her. That it wouldn't be so easy to get rid of, you know, of womanhood, that it was coming back for her.''