It turns out "I'll be there for you" was not just a line in the "Friends" theme song.

Jennifer Aniston, Courteney Cox and Lisa Kudrow starred as the female leads in the beloved sitcom, and 19 years after the show went off the air, they are proving they are just as close as their characters were, with heartwarming Instagram posts celebrating Kudrow's 60th birthday.

Aniston shared a series of photos of her with Kudrow over the years, and in her caption she wrote, "Please join me in celebrating one of my favorite people on the planet. LISA KUDROW!!"

‘FRIENDS’ STAR LISA KUDROW TURNS 60: WHAT FANS DIDN'T SEE ON HIT SHOW

A photo of Courteney Cox, Jennifer Aniston, Lisa Kudrow

From left to right, Courteney Cox, Jennifer Aniston and Lisa Kudrow have remained close over the years since "Friends" ended. (Gregg DeGuire/Getty Images for SAG-AFTRA Foundation)

"She’s been my friend and my family for nearly 30 incredible years," she continued. "I cherish you…I love you, my sweet Floosh. One of the most talented comedians/actors I’ve had the great honor to work with for all these glorious years and more to come!"

She told her followers, "Happy Lisa’s Birthday!"

A photo of the cast of "Friends"

Pictured clockwise from bottom left, Courteney Cox Arquette as Monica Geller, Matt LeBlanc as Joey Tribbiani, Lisa Kudrow as Phoebe Buffay, David Schwimmer as Ross Geller, Matthew Perry as Chandler Bing and Jennifer Aniston as Rachel Green. (Reisig & Taylor/NBCU Photo Bank/NBCUniversal via Getty Images via Getty Images)

Aniston's nickname for Kudrow is Floosh, she previously revealed, while Kudrow's nickname for her is Joo. This was reflected in Kudrow's response to the post.

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"My Joooiest Joooo I love you beyond my dear friend forever!" she exclaimed.

Cox also shared a number of pictures, but it seems she originally tried to use AI to send Kudrow a birthday message.

Cast of Friends drinking milkshakes

From left to right, Matthew Perry as Chandler Bing, Jennifer Aniston as Rachel Green, David Schwimmer as Ross Geller, Courteney Cox as Monica Geller, Matt Le Blanc as Joey Tribbiani and Lisa Kudrow as Phoebe Buffay. (NBCU Photo)

"Happy Birthday my Loot," she wrote. "This is my second attempt: ChatGPT didn’t give you nearly the amount of love I feel for you."

"You are the smartest, funniest, most thoughtful person. I always feel seen and loved when I’m around you. That’s the gift you give to those you love," she stated.

"Friends" fans got insight into another set of special nicknames here – Cox called Kudrow Loot, and in turn Kudrow called her Cahoot.

Friends cast sitting in front of the fountain featured in their opening credits

The theme song used for "Friends" was originally only written as a 45-second song, however it became so popular, The Rembrandts wrote a full version. (Photo by Reisig & Taylor/NBCU Photo Bank/NBCUniversal via Getty Images via Getty Images)

The actress replied with, "Oh Cahoot. I love You so much and guess what? I always feel seen by YOU."

The three stars met when they were cast on the massively popular sitcom in 1994. Aniston played the role of Rachel Green, Cox was Monica Gellar and Kudrow played Phoebe Buffay.

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Opposite them were the male leads – David Schwimmer as Ross Gellar, Matthew Perry as Chandler Bing and Matt LeBlanc as Joey Tribbiani.

Jennifer Aniston and Lisa Kudrow in all-black outfits show up to support Courteney Cox who is receiving her Star on the Walk of Fame, also wearing black, holding her star plaque

Courteney Cox's "Friends" co-stars Jennifer Aniston and Lisa Kudrow showed up to support her at her Walk of Fame ceremony. (Gilbert Flores/Variety)

While the men did not send Kudrow public well wishes for her birthday, there is no denying the closeness of the entire cast.

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When the show was still on the air, Schwimmer and Aniston famously took a pay cut so that all six of the principal actors would make the same amount of money per episode, and just earlier this year, Aniston and Kudrow showed up to support Cox as she received a star on the Hollywood Walk of Fame.