The 47-year-old actor appeared to confirm on Monday that his oldest child, Indiana, is leaving home by posting an emotional Instagram post.
"The sea is vast, the water gets deep, and the winds might pick up. You've witnessed it before. Although a ship is most secure in port, that is not what ships are designed for, the Oscar winner wrote in the caption of a throwback image of him and the now-18-year-old.
You are prepared for this, Affleck continued in his letter. "You are exceptional and wonderful; you are honest, brave, and kind. You will make the realm of "grownups" better.
"And the world will (finally) greet you with the same if you walk out into the world with inquisitive wonder and true thanks," he said.
The director concluded his message to the teen by saying, "Please remember that one of the best parts of any experience... is going home. I cherish you.
Indiana will adore "the dorms" at college, according to one of Affleck's supporters, who also added, "My son is leaving for university too."
The finest aspect of parenting, according to a third commenter, is seeing your children blossom. Letting go is the most difficult.
Indiana turned 18 in June, but Affleck hasn't said whether she's starting school or just leaving home. He commented, "I have always looked up to you," next to a photo of the two of them trekking. "I believe I will always. 18."
In addition, the "Manchester By the Sea" actor and his ex-wife, Summer Phoenix, are parents to 14-year-old Atticus. Affleck moved on with Caylee Cowan after the ex-couple declared it quit in 2017.
The Golden Globe winner said of the 24-year-old actress during their January anniversary, "We have experienced a lot of highs and lows this year, but how I feel about you has only gone in one direction."