A YouTube video shared by a fan on Friday finds Joel pointing out at Brinkley, who was in the crowd, while singing his iconic track, "Uptown Girl."
The 65-year-old Piano Man and the model were married for nine years before their August 1994 divorce. They have a 25-year-old daughter named Alexa Ray Joel.
Brinkley, 60, appeared in the original video for "Uptown Girl" in 1983 two years before she married the singer. While at the show, the model took to Instagram to share a photo of herself and her daughter in the audience and titled it: "He's still got it."
Joel announced he'd be playing one monthly show at Madison Square Garden starting December 2013.
"Playing Madison Square Garden is an experience that never gets old," Joel said at the time. "A show a month at the Garden for as long as there's demand means more opportunities to connect with music fans and provides a unique and memorable show every time we play here."