Affleck's posts included several sweet photos of Garner, 49, with their children over the years. The two are parents to 15-year-old daughter Violet, 12-year-old daughter Seraphina and 9-year-old son Samuel.
"So happy to share these kids with you. Luckiest parents in the world. Thanks for all the good you do," Affleck wrote. "Happy Mother's Day. Love, their Dad."
Affleck and Garner have remained on good terms since their split in 2015, though he recently made headlines for a reunion with another ex. The actor reconnected with Jennifer Lopez late last month, and a source told ET how Garner felt about it.
"Jen isn't bothered by Ben hanging out with J.Lo or anyone else. She wants what is best for Ben," the source shared.
"What matters most to her is Ben being a great dad," the source continued. "They've been in a good groove when it comes to co-parenting for a while and their kids' happiness is Jen's main priority."
As for the status of Affleck's relationship with Lopez, a source said the former engaged couple is now just friends.
"They obviously have a romantic history, but at this point they only have a friendship," the source said. "They both admire each other professionally, respect one another and feel comfortable with each other."
A second source told ET: "Jennifer and Ben have seen each other a few times since her breakup with Alex. Jen and Ben have remained friends over the years and the two are still just that - friends."
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