"Happy birthday Bridget Moynahan," Brady posted Wednesday on his IG along with a 2018 photo of the actress with their son, Jack ... "We hope you have a great day."

Remember, Moynahan gave birth to Jack after they broke up back in 2006 -- a few months after Brady began dating Gisele.

Everybody involved has publicly acknowledged the situation was challenging at first -- but over the years, they've essentially become one big happy family.

Tom has since had 2 more kids with Gisele. Bridget married Andrew Frankel in 2015.

Jack made headlines earlier this year when he shared an unbelievably sweet moment with Tom after the QB's Bucs team won the NFC championship game back in January.

Tom and Jack hugged it out and swapped "I love you's" in a video that went viral within minutes!