Casey Anthony's Former Fling Reacts to News of Her New Partner

A guy who had a quick fling with Casey Anthony is weighing in on her latest romance with a former cop ... saying he feels no ill will toward her despite cutting things off once he found out about her infamous murder trial.

Antony Karagiannis -- who hung out with Casey a couple times back in 2018 -- tells TMZ ... he hasn't kept tabs on Casey's budding relationship with New Hampshire gun store owner Ben Beauchemin ... but he shared a short and sweet message to them -- "Good luck to both of them." Karagiannis says he hopes Casey finds peace and happiness "with whatever she has left in her life."

As for their relationship, Karagiannis makes it clear he and Casey were never an item -- just two people who casually hung out -- and had a one-night stand.

First, he says, they grabbed a drink after his bar shift in Florida one night. On another night, Karagiannis says, they went for cocktails with his friends at another saloon in West Palm Beach to watch the Yankees game. At some point, Karagiannis claims, he hooked up with Casey.

Karagiannis also says Casey seemed like a nice woman ... but once he found out Casey was charged with her daughter Caylee's murder and later acquitted at trial, he promptly cut ties with her. He goes on to say, "Whatever happened with her and her kid, she's going to take that to the grave with her."

As we reported ... Casey and Ben B. were tossing back Bud Lights and chowing down on bar food Wednesday in Manchester, NH. Our sources tell us Ben owns gun shop called Wicked Weaponry, and is a former police officer with the Hooksett PD, and he's an Army vet.