KATIE HOLMES has recon­nected with former flame Fringe star JOSHUA JACKSON – and sources say the hunk’s longtime GF, actress DIANE KRUEGER, isn’t happy about it.

Katie, 33, and Joshua, 34, were a couple on-screen and off while film­ing the teen drama “Dawson’s Creek,” and he recently revealed that Katie reached out to him after divorcing su­perstar Tom Cruise.

Now insiders say “Troy” beauty Diane, 36, isn’t happy with the relationship.

“Diane has been dating Joshua since 2006 – just around the same time Katie married Tom,” an insider told The ENQUIRER.

“Even though Joshua’s rela­tionship with Katie only lasted a year, Diane knows that it burned red-hot. I think that bothers Diane deeply.”

Joshua, who now stars on the FOX show “Fringe,” once told pals: “Katie told me I was her first love and she would treasure it forever.”

And Diane was said to be upset after Joshua confessed on the Canadian talk show “George Stroumboulopoulos Tonight” that Katie had tele­phoned him.

“Like any old friend, it was like, ‘Oh, hi, how are ya? What’s going on? I had a kid,’” Josh­ua said, referring to Katie’s daughter Suri, 6.

The chat was “nice,” he added. “It was very nice actually.”

And THAT won’t sit well with Diane.

“That kind of talk will have Diane green-eyed with jealousy,” revealed the insider. “I think she wants Katie as far away from her man as possible so she doesn’t get a chance to steal him back!”