Watch Sean Penn's Sweet Reaction to Madonna Performing Song He Inspired

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What a difference a few decades can make on a relationship.

Madonna and Sean Penn had a pretty tumultuous divorce in 1989, but 26 years later, they're vying for the title of friendliest exes in Hollywood!

WATCH: Madonna Spanks Amy Schumer at Rebel Heart Concert

On Thursday night, Penn was spotted by an ET insider enjoying the second night of Madonna's Rebel Heart tour at Madison Square Garden in New York City. The 55-year-old actor didn't even appear awkward when the Material Girl performed her hit, "True Blue," which was inspired by him.

In fact, Madonna's former husband had a sweet smile on his face!

Madonna actually dedicated the entire True Blue album to Penn in 1986. "This is dedicated to my husband, the coolest guy in the universe," she wrote in the liner notes.

During her show, the 57-year-old music icon also admitted that she's not sure if she'll ever wed again. (She was married to director Guy Ritchie from 2000 to 2008.) Madonna joked that all the married and in love people in the audience were "suckers." She added, "But I'm still a romantic heart."

MORE: Madonna's Son Rocco Dresses Up as Sean Penn's Fast Times at Ridgemont High Character!

Penn wasn't the only famous face at Madonna's concert. Jeremy Scott, Zac Posen, Andy Cohen, Kelly Ripa and her husband, Mark Consuelos, were all in attendance.

Ahead of her 57th birthday in August, Madonna shared a flashback photo of her getting a kiss from Penn. "Its almost our birthdays!! 2 Leo's ❤️#rebelhearts," she Instagrammed.

Penn has also opened up about getting along with his former spouse. He told Esquire U.K. in a January interview, "I'm very friendly with my first ex-wife."