Harry Styles and Florence Pugh in Don't Worry Darling. Photo / Supplied

Harry Styles reportedly kissed co-star Florence Pugh on the set of their film Don’t Worry Darling weeks before his relationship with director Olivia Wilde began.

The kiss is rumoured to be the reason Florence and Olivia “fell out” during filming, reports the Sun.

A source told the publication, “Harry and Florence had chemistry from the off, which translated incredibly well on-screen.

“One night they had a bit of a snog, all very light-hearted and a bit of fun, and that was that.

“It was being gossiped about by a couple of members of production, otherwise no one would have known.

“Harry was very much single at the time and Florence had separated from Zach Braff, although she’d kept the split quiet to — ironically — avoid headlines.

“There was no cheating or misbehaviour from anyone.

“However, later on, Harry and Olivia started spending more time together — sneaking off for coffees, hanging out in one another’s trailers, and sharing small, routine intimacies.

“It was clear to all they had a real connection. When they were pictured holding hands for the first time, Florence wasn’t too happy.”

In Pugh’s only interview to promote the thriller, she appeared to take a stab at Wilde for using one of the film’s most intimate scenes in the trailer.

“When it’s reduced to your sex scenes...to watch the most famous man in the world go down on someone ... it’s not why we do it. It’s not why I’m in this industry,” she said.

Then leaked messages in which Shia LaBeouf, who was originally cast in Styles’ role, appeared to show Wilde patronising Pugh, adding to the tension.

Pugh skipped a scheduled group interview ahead of the film’s Venice premiere, arriving just minutes before the screening started.

Meanwhile, a former nanny for Wilde and her former partner Jason Sudeikis has echoed the claims there was a fling between Pugh and Styles that began a couple of weeks after the former One Direction star joined the cast.

“Then Olivia started seeing Harry herself. It was all very quick,” she said.

“There was already tension between the two women and this undoubtedly fanned the flames.

“Although the feud is one of Hollywood’s worst-kept secrets, everyone involved is a professional and things are now cordial.”

The rumours first surfaced in August this year. However, at the time, Pugh was said to have simply “deplored their habit of taking private time together in trailers during filming”.