Ariana Grande Cheers on Boyfriend Ethan Slater at First Performance of Broadway's “Spamalot ”Revival

A source tells PEOPLE that Grande has been a “big supporter” of the production and “already has plans to go again"

Ariana Grande is her boyfriend Ethan Slater’s No. 1 fan.

On Tuesday, the 30-year-old singer was spotted cheering on Slater, 31, during the first preview performance of Broadway’s Spamalot revival at the St. James Theatre in New York City.

In an Instagram video shared by show attendee Jim Glaub, the pop star could be seen watching and smiling from the audience as colorful confetti fell and those around her clapped and cheered.

A source tells PEOPLE that Grande has been a “big supporter” of the production and “already has plans to go again.”

“She has seen it during tech rehearsals,” the insider shares. “She was so sweet last night, taking pictures with fans and gushing about how much she was enjoying the performances. She's a theater kid at her core, so you see she really feels at peace being around Broadway."

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Related: Ariana Grande and Ethan Slater's Relationship Timeline

The “7 Rings” hitmaker attended Tuesday’s performance with her brother Frankie Grande and friend Doug Middlebrook, and she was later snapped leaving the show’s opening night with Middlebrook.

In the photos, Grande could be seen smiling as she placed a paper Spamalot crown on her head and carried a program for the show. Middlebrook, who dressed up in a knight’s costume, also got playful at one point and laughed as he placed a crown on the musician, who sported a beige dress, brown coat and boots and white lace gloves.

Back in August, production announced that Slater was set to star in the musical in the dual role of The Historian/Prince Herbert.

He and Grande met on the set of the upcoming movie adaptation of Wicked, and developed a romance offscreen. Slater, who made his Broadway debut in SpongeBob SquarePants: The Broadway Musical, will play Boq, the love interest of Elphaba’s sister Nessarose who is infatuated with Glinda (played by Grande).

Grande also got her start on Broadway, starring in Jason Robert Brown's short-lived 2008 musical 13. On Sept. 30, she once again returned to her theater roots when she visited the Stephen Sondheim Theatre to sit in the audience of the Tony-nominated musical & Juliet.

Related: Ariana Grande's Boyfriend Ethan Slater Joins SAG-AFTRA Picket Line in New York City amid Strike

Grande and Slater’s relationship, which was first confirmed by PEOPLE in July, began after her separation from husband Dalton Gomez and Slater’s separation from wife Lilly Jay.

Last month, Grande and Gomez, 28, settled their divorce just weeks after filing, following two years of marriage.

Since Grande and Slater’s romance became public, the couple has tried to keep their relationship out of the spotlight and keep things low-key.

As a source told PEOPLE in September, “They are just trying to navigate their new relationship in private."

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