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

Olivia Wilde and Harry Styles Seen Holding Hands as Source Says 'They Have Dated for a Few Weeks'

Olivia Wilde and Harry Styles were seen holding hands at a wedding and later arriving at his L.A. home

Olivia Wilde and Harry Styles are growing close while filming their upcoming movie together.

The pair, who have been dating for a "few weeks," PEOPLE reported Monday, are collaborating on Don't Worry Darling, Wilde's highly-anticipated directing followup to 2019's Booksmart. Wilde and Styles both star in the film, which Wilde is directing.

A source tells PEOPLE their relationship evolved while making the drama.

"What started out as a close friendship, quickly turned romantic," the source says. "Everyone saw it coming. During breaks, he's hasn't been able to stay away and visited her trailer."

Styles, 26, was seen visiting Wilde's trailer during filming, standing just outside the door wearing a mask while Wilde, 36, leaned out to chat with her star. Wilde was seen smiling several times as the two remained in costume for the movie.

RELATED: Olivia Wilde and Harry Styles Seen Holding Hands as Source Says 'They Have Dated for a Few Weeks'

Backgrid Harry Styles visits Olivia Wilde's Trailer on the set of "Don't Worry Darling"

The 1950s-set film stars Florence Pugh as a housewife who discovers a disturbing truth while living in an isolated community in the California. Styles, who stars as Pugh's character's husband, replaced original star Shia LaBeouf shortly before filming started.

The movie is written by Katie Silberman, Wilde's Booksmart collaborator, based on an original script by the VanDyke brothers.

John Shearer/Getty; Dia Dipasupil/FilmMagic

The pair were seen holding hands at a friend's wedding over the weekend. A source told PEOPLE "they have dated for a few weeks."

"They were in Montecito, California this weekend for a wedding," the source said. "They were affectionate around their friends, held hands and looked very happy."

A rep for Wilde could not be immediately reached for comment, and a rep for Styles has not commented.

RELATED: Harry Styles Debuts Slick New Hairdo on the Set of Upcoming Film Don't Worry Darling

Rachel Murray/Getty; Dia Dipasupil/Getty

In Styles' recent cover story for Vogue's December issue, Wilde explained why she was so excited for the "Watermelon Sugar" singer to bring his enthusiasm to her "incredibly stylistic" movie. Don't Worry Darling counts on Academy Award nominee designer Arianne Phillips (A Single Man) for costume design.

“She and I did a little victory dance when we heard that we officially had Harry in the film, because we knew that he has a real appreciation for fashion and style," Wilde said of her and Phillips' reaction. "And this movie is incredibly stylistic. It’s very heightened and opulent, and I’m really grateful that he is so enthusiastic about that element of the process—some actors just don’t care.”

“To me, he’s very modern,” said Wilde of Styles, “and I hope that this brand of confidence as a male that Harry has—truly devoid of any traces of toxic masculinity—is indicative of his generation and therefore the future of the world. I think he is in many ways championing that, spearheading that. It’s pretty powerful and kind of extraordinary to see someone in his position redefining what it can mean to be a man with confidence.”