AceShowbiz -

Angelina Jolie is "pretty upset" about romance rumor surrounding her estranged husband, Brad Pitt, and 21-year-old actress Ella Purnell. The "Salt" actress, who split from the "Allied" actor a year ago, is reportedly not happy that he has his eyes set on the aspiring British actress, who happened to be Jolie's co-star in 2014's "Maleficent".

A source reveals to HollywoodLife.com that news of the 53-year-old actor being "interested" in Purnell is "not sitting well" with the mother of six. "Angelina's heard the buzz about him being interested in this actress and it's not sitting well with her," says the source, before revealing that the big age gap between the two is a factor.

"The girl is so young, she's barely in her twenties for heaven's sake," says the source. The 42-year-old actress allegedly has "been assured by a number of people that there's nothing to the rumors but it's still got her pretty upset. The age gap is the biggest factor. She'd be incredibly disappointed in Brad if he went down that road."

As reported before, Pitt is "so enchanted" with Purnell. "Brad had Ella in mind from the get-go. He went out of his way to cast her," a source told In Touch. "Ella is incredibly flattered by all the attention she's getting from Brad," the source added. "She's told friends he's always been her No. 1 celebrity crush."

"He realizes the huge age difference," said to the source, "and that everyone would look at the relationship as a midlife crisis mistake." However, Pitt's attraction is more than just physical, according the insider, who revealed, "He's taken with Ella's spunky, funny demeanor and formidable acting skills."

"Although Brad's been working on his sci-fi space travel film 'Ad Astra', he's been checking in with Ella weekly as she preps for production," the insider claimed, adding that "Brad plans on coaching Ella for the show. He's sure it's going to be a hit and that it's going to make Ella a star." While things between them remain platonic at the moment, that won't last long, the source predicted. "It's only a matter of time before Brad takes their relationship to the next level," the insider noted.