Harry Styles & Olivia Wilde’s 'Chemistry Was Very Obvious' on Movie Set but They Were 'Professional': Source

Harry Styles and Olivia Wilde's new romance might have come as a shock to fans, but those on the set of their upcoming film, Don't Worry Darling, weren't surprised by the news.

In this week's issue of PEOPLE, on newsstands Friday, sources says the actress-director, 36, struck up a close friendship with the singer, 26, last fall as they began work on her highly-anticipated sophomore directorial project, which she also stars in.

As they spent time together on-and off-set, their friendship "quickly turned romantic," says an insider. "Their chemistry was very obvious."

Wilde — who split from fiancé Jason Sudeikis, 45, in early 2020 — brought on the former One Direction singer as the film's male lead in September. He plays the husband of Florence Pugh's character, a 1950s housewife who discovers a disturbing truth while living in an isolated community in California.

"I did a little victory dance when we heard that we officially had Harry in the film," Wilde told Vogue for its December issue.

RELATED: Olivia Wilde and Harry Styles' 'Close Friendship Quickly Turned Romantic' on Movie Set: Source

After conservative commentator Candace Owens slammed Styles in November for wearing a dress on the magazine's cover, Wilde was among many who jumped to his defense, calling Owens "pathetic" on Twitter.

"Olivia was going on and on about how wearing a dress still makes Harry masculine," says the insider. "It was again just so obvious she had fallen for him."

Meanwhile Styles — whose former flames include Taylor Swift, Kendall Jenner and, most recently, model Camille Rowe — is just as smitten.

"During breaks in filming he wasn't able to stay away and would visit her trailer," says the insider. (On Nov. 3, Styles was photographed stopping by Wilde's trailer for a chat.)

After Wilde and Styles were seen holding hands at a friend's wedding in Montecito, California, over the weekend, a source confirmed to PEOPLE that "they have dated for a few weeks."

Despite their budding romance, the two continue to keep things "very professional" at work.

"Olivia and Harry created this loving and warm environment," says the insider. "Everyone loved working with them. She takes her work very seriously, but everyone saw it coming."

For all the details on Harry Styles and Olivia Wilde's surprise romance, pick up the latest issue of PEOPLE, on newsstands Friday.