The actor posted a loving tribute to both ladies Sunday, saying ... "Happy Mother’s Day to the two incredible mothers who have shown me the meaning of love."
He continued by vowing to make two donations in their honor -- one to Cut50's Dignity for Incarcerated Women Campaign, which aims to reduce prison populations, and to National Bailout ... an org that works to bail out black mothers and caregivers who are locked up and detained in pre-trial detention because they can't afford to pay their way out of jail.
It sounds like both Jen and his mom, Christine Anne Boldt, are backers of those causes, so it's gotta mean a lot that Ben's gonna put some dollars toward them.
As to why Ben is shouting out his ex on Mother's Day ... it's no secret that she's been there for him through thick and thin, even in the wake of their drawn-out divorce.
Class acts all the way around in this fam.