Marc Anthony -- Bro Huggin' It Out with Jennifer Lopez's BF Casper Smart

Marc Anthony isn't just on good terms with his estranged wife Jennifer Lopez ... he's also on good terms with the guy who's bangin' her ... at least judging by this photo.

TMZ has obtained a photo of Casper Smart in a great, big bro hug with Marc at a private airport in NY yesterday.

We're told the kids -- Emme and Max -- have been hangin' with J.Lo and Casper during the most recent leg of Jenny's international tour ... and when they arrived back in the States on Monday, daddy was right there to greet them.