Ariana Grande Seen Cheering on Boyfriend Ethan Slater at Launch of Intimate Shows in N.Y.C.

The 'Wicked' star was seen giggling at Café Carlyle as boyfriend Ethan Slater performed songs and told funny stories about his life and "year of great change"

She's a stan!

Ariana Grande was seen enjoying an intimate performance by her boyfriend Ethan Slater, who kicked off his weeklong residency at Café Carlyle in New York on Tuesday, May 28.

"She was laughing at all of his jokes in between songs, and cheering for him after each song," an onlooker tells PEOPLE, who says the Spamalot star sang hits from Broadway shows like Fiddler on the Roof and Pippin, as well as a selection of original tunes and some Bob Dylan covers.

He also did two acoustic covers from his SpongeBob SquarePants musical, which he starred in during its 2018 Broadway run, and between songs made references to his "big year of change."

Related: Who Is Ariana Grande's New Boyfriend? All About Her 'Wicked' Costar Ethan Slater

"He's extremely talented," the source continues of Slater, 31, who will be playing Boq in the upcoming big screen version of Wicked, which is slated for a Nov. 27 release.

"The show was mostly about him and his love of music and theater, though he did steal a quick glance over to Ariana when he sang a line about being 'Lucky to be in love.' It was very cute."

Related: Wicked First Trailer: See Ariana Grande and Cynthia Erivo in First Footage from Movie Musical

The source continues, "He did talk about Wicked, and at one point he acted like he was going to cover "Defying Gravity" and it seemed like the crowd hoped Grande would join him onstage, but then he did a last minute switch into "If I Only Had a Heart" from the original Wizard of Oz movie. Everyone was laughing."

The source says Grande seemed to be having a great night with her small group of friends.

"She was so sweet, smiling at everyone who caught her eye, and having a nice dinner with a small group of friends in one of the banquettes at the back. It was a very intimate crowd, mostly full of theater fans. Nobody was bothering her."

The onlooker notes Grande even joined in with the other guests to wish one of the patrons a happy birthday when a dessert with a candle came out for her.

Related: Ariana Grande Is Dating Her 'Wicked' Costar Ethan Slater After Dalton Gomez Split: Sources

In December, a source told PEOPLE that Grande and Slater, who met on the set of Wicked and began dating last July, were not only going strong, but getting serious.

“Ariana is serious with Ethan," the source said. "She loves being with him."

Grande was also a fixture at his Spamalot shows during Slater's run playing The Historian/Prince Herbert in the Broadway musical.

"They love to support each other in their work," the source said. "When she’s done with work, Ariana loves going to the theater when she can."

Slater will perform four more shows at Café Carlyle this week.

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