Ariana Grande Shares Loving Tribute for 'Victorious' Costar and Longtime BFF Liz Gillies' 30th Birthday

"You have made my heart so unfathomably happy and whole these past 16 years," the Grammy-winning singer said of the 'Dynasty' alum

Ariana Grande is helping her longtime best friend Liz Gillies feel all the love on her milestone birthday.

As Gillies turned 30 on Wednesday, the "7 Rings" singer celebrated her Victorious costar with a loving Instagram Story tribute.

"Happy birthday to the most beautiful, brilliant, talented, funniest person I've ever met in my life @lizgillz," Grande, 30, captioned a candid selfie of the pair.

"You have made my heart so unfathomably happy and whole these past 16 years!" she continued. "Absolutely everything and also, absolutely nothing has changed. I love you more than words can possibly express and I hope we can be best friends in every life."

Related: 'Victorious' Alum Elizabeth Gillies Explains Why She Wasn't at Pal Ariana Grande's Intimate Wedding

Grande and Gillies first met as children starring in the Broadway production of 13. Many years later, they became costars again in Nickelodeon's Victorious, which ran for four seasons from 2010 to 2013.

The pair continued to remain close over the years, with Grande even tapping the Sex&Drugs&Rock&Roll alum to appear in her "Thank U, Next" video in 2019.

"We're totally close. She's like blood to me, she's like my sister," Gillies previously told PEOPLE of the Grammy winner in 2015. "So unless we have a massive falling out, nothing will be happening there. We lived together, I've known her since what feels like the beginning of time."

Related: All Grown Up: 9 Child Stars Who've Had Dramatic Transformations

Gillies began celebrating her third decade of life ahead of Grande's sweet tribute. Three days before her birthday, the Dynasty alum shared a carousel of photos from an intimate gathering with friends, featuring herself with a cake and shots of herself showing off her chic, black cutout dress.

"3 days 'till 30 🍸💀" she captioned the post.

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Some of Gillies' Dynasty castmates showed some love in the photo carousel's comments section. "My little girl is growing up! I love you Lizzy. 💖" said her former TV mom Elaine Hendrix, while Rafael De La Fuente wrote, "You’ve never looked better! ❤️"

Gillies also shared photos from her "lil trip with Mama" the day before her birthday.

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