Richard Simmons' death was mourned by celebrity tributes led by Pauly Shore, Denise Austin, and Ricki Lake.

Richard Simmons' sudden death on Saturday has left many celebrities in mourning, including Pauly Shore, Denise Austin, and Ricki Lake.

One day after celebrating his 76th birthday, Simmons, the creator of "Sweatin' to the Oldies" workout videos, passed away. His longtime representative, Tom Estey, confirmed his death to Planet Chronicle Digital.

Following the announcement of Simmons' passing, Shore honored the fitness expert on X, calling him "irreplaceable."

The 56-year-old comedian wrote that he learned about Richard Simmons' passing like everyone else.

I hope you're at peace and twinkling up in the heavens. Kindly give my mother Mitzi and my father Sammy a big hug and a kiss for me.

"Richard, you are unique and have had an incredible life. Your story is remarkable. They accidentally cut your dolphin shorts when they were making you. May you rest in peace, my dear friend. May you rest in peace."

An upcoming biopic about Simmons is being produced by Warner Bros. subsidiary the Wolper Organization and written by Jordan Allen-Dutton, with Shore set to star as Simmons.

In May, Shore confirmed that the project is moving forward, despite Simmons expressing his disapproval in April and stating that it did not have his blessing. Simmons had claimed that he was "up all night crying" due to Shore's reaction, but later confirmed that the project was proceeding.

Simmons' longtime friend, Denise Austin, paid tribute to the late aerobics instructor in a heartfelt Instagram post.

She expressed her grief over the passing of her dear friend and colleague, Richard Simmons, by writing alongside an image of the two of them smiling.

I am devastated because Richard is someone I have known and started the aerobics business with over 40 years ago. Every time we were together, we had so much fun, filled with hugs, laughter, and tears. I will never forget Richard singing through the hallways, hugging my daughters, and even sending me a letter when my mom passed.

"Denise cherished her friendship with Richard and can't believe she reached out to him less than a month ago. Richard left an impact on all of them, and Denise thanks him for all his love. They did so much together in life, and Denise loves him so much. Richard will forever be in her heart. Love, Denise."

Ricki Lake shared a photo with Simmons and Maria Menounos, expressing her grief over the loss of a "super special human" with the caption "RIP."

The TV personality, who is 55 years old, broke her heart with the addition of a love emoji while expressing how much she loved him.

Simmons was a guest on "The Ricki Lake Show," which aired from 1993 to 2004 and featured Lake as the host.

Sally Jessy Raphael paid tribute to Simmons by sharing a throwback photo of herself with the "Weight Saint" on X.

"Raphael, 89, who hosted the long-running tabloid talk show "Sally" which was originally named "The Sally Jessy Raphael Show," wrote that he is completely devastated at the loss of @theweightsaint. They had done so many shows together, shared so many laughs & hugs, and he considered him a dear friend who changed so many lives over the years."