Ben Affleck would like you to know that Matt Damon is his BFF. On the occasion of National Best Friends Day, the actor posted a humorous photo on Instagram of the time Damon shoved birthday cake in Affleck’s face. It was captioned: “This Guy #NationalBestFriendsDay.’’ It’s not clear when the picture was taken, but judging from Affleck’s sweet ’90s hairstyle, it could be around the time of “Good Will Hunting’’ in 1997.

Affleck and Damon have been friends since childhood, growing up in Cambridge together, and attending Cambridge Rindge and Latin. The two co-wrote and starred in “Good Will Hunting,’’ which went on to win an Oscar for best original screenplay.

Heather Ciras can be reached at heather.ciras@globe.com. Follow her on Twitter @heatherciras.