The pair are co-starring in Quentin Tarantino’s Once Upon A Time In Hollywood, which has just started production in Los Angeles.
According to an on-set observer, Brad is clearly smitten with the Aussie beauty.
An insider told Radar Online: "Brad is very taken with Margot, and their chemistry is the talk of the cast."
Sadly for Brad, however, the actress is happily married to Tom Ackerley, whom she wed in 2016.
It’s not the first time Brad’s feelings for Margot have been reported. His crush on the actress was revealed in 2016, a year after he apparently ensured she had a small part in The Big Short, which he produced.
Despite his then-wife Angelina trying to block the move, Brad cast Margot in the memorable cameo role, which saw her give a sexy finance tutorial while in a bubble bath.
At the time, a source told Hollywood Life: "Brad has had his eye on Margot for years. He jumped at the chance to squeeze her into the role she had in The Big Short so that he could spend time with her."
Their paths have crossed a few times since then, including when a very happy looking Brad stepped out of his post-divorce isolation to attend a Chateau Marmont pre-Oscar party that Margot was also attending back in March.
But now they’re back together filming a thriller based on the Manson murders, Brad’s admiration for the former Neighbours star has amped up again.
Apart from having "all the qualities he loves in a girl", the set insider adds that "if she wasn’t married there’s no doubt whatsoever he’d be asking her out in a heartbeat".
"They get along very well, and Brad’s super excited to be working with her, more than he’s been in years with a leading lady," says the source.
Meanwhile, film producer Tom, 28, is being warned he has reason to worry.
"This has to be hard for Tom, who’s a trusting guy, but anyone in his position would find it tough," the insider adds.