Denise Austin still has fond memories of her pal Richard Simmons.

After decades in the spotlight, the fitness guru suddenly stopped teaching at his workout studio in 2014 and has now retreated from public life altogether. In August, FOX aired "TMZ Investigates: What Really Happened to Richard Simmons," a special that explored his rise to stardom and surprising departure. It featured interviews with Austin and Suzanne Somers, as well as friend Bruce Vilanch and Simmons’ longtime costume designer Leslie Wilshire.

"Oh my gosh, we had so much fun together," Austin told Fox News Digital. "He would hug me every single time we ever got together. He was so kind and so sweet – just the greatest guy. And he loved my daughters who still always ask about him."

Richard Simmons and Denise Austin fitness pals

Richard Simmons and Denise Austin found fame around the same time as fitness stars. (Photo by Brian To/FilmMagic)

"I adore him," the 65-year-old continued. "It was fun to start a career around the same time he did. And you know, I’ve done it now for 40 years. He was a big part of it. It was really fun to be around him. We just loved motivating people. That’s what makes him shine. We both want to feed people our positive energy. And I do it because everyone needs it. Everyone wants to have someone who is encouraging and uplifting. Someone who will tell you, ‘You’ve got this, you can do it. I promise you that when you’re done, you’ll feel so much better.’"

FITNESS ICON DENISE AUSTIN, 65, REFLECTS ON ROCKING A BIKINI FOR SI SWIMSUIT RUNWAY: ‘IT'S NEVER TOO LATE'

For decades, Austin has been encouraging people to kick off an active lifestyle through her workout routines. She has sold more than 24 million exercise videos and DVDs. She also led the longest-running fitness show in TV history. Most recently, she teamed up with Easy Spirit to launch a new collection titled "Easy Spirit x Denise Austin."

The fitness star said she loves reminiscing about her time with Simmons, 74 – but she does not love remembering everything from the past.

Denise Austin fitness '80s

Fitness guru Denise Austin jumping during a fitness routine at home, circa 1980s. (Photo by Diana Walker/Getty Images)

"The first thing that comes to mind is my hair," Austin chuckled when talking about the aerobics era of the ‘80s. "And what I wore – oh God, I used to wear a leotard with no tights! Sometimes with just some little leg warmers. I had to film my TV show with a leotard without tights – three months after each baby was born."

"I gained 35 pounds with each baby," she shared. "I just put on my leotard and went for it. But you know, when I think about [that era], it reminds me of the fun times of just starting out and knowing the sky’s the limit. You know, that feeling you have when you’re young. I think we all had that."

CLICK HERE TO SIGN UP FOR THE ENTERTAINMENT NEWSLETTER

In 2020, Austin told TMZ she has been in constant contact with Simmons’ managers, and they assured her he is doing well.

Richard Simmons and Denise Austin honor Jack LaLanne

Fitness gurus Richard Simmons and Denise Austin at Jack LaLanne's funeral service on Feb. 1, 2011, in Los Angeles. LaLanne was known as the ‘Godfather of Fitness' who invented the first modern exercise machines and popularized workouts and healthy eating. Austin told TMZ she has stayed in touch with Simmons' managers over the years who've assured her he is doing just fine. (Photo by David McNew/Getty Images)

Following the TMZ special, Simmons took to Facebook and thanked his fans for their support.

"Thank you everyone, for your kindness and love," he captioned his post with a smiling emoji holding a thank-you sign. "Love, Richard."

The star’s sudden departure from the spotlight previously sparked a podcast titled "Missing Richard Simmons," as well as numerous conspiracy theories alleging he was being held hostage in his Hollywood Hills home by his housekeeper.

RICHARD SIMMONS LEFT THE SPOTLIGHT FOR THIS REASON, DOC CLAIMS: ‘HE'S JUST NOT THE SAME GUY ANYMORE’

Richard Simmons fitness day

Richard Simmons left the public eye nearly a decade ago. (Photo by Moses Robinson/Getty Images)

In 2017, Simmons sued two tabloid publications that alleged he was transitioning into a woman. Attorneys for Simmons have said he supports transgender rights, but the allegations defamed him.

According to the doc, there is a surprisingly simple reason why Simmons retreated from the spotlight.

"Doctors told him back in 2014, around the time he disappeared, that he needed a left knee replacement," the doc alleged. "And if he didn’t get one, he might never be able to exercise again. Now, this is key to the disappearance of Richard Simmons. The prospect of surgery, of becoming sedentary, caused Richard to sink into a deep depression. We know still to this day Richard still hasn’t gotten corrective surgery on his left knee. He walks with a cane and that explains a lot. He’s just not the same guy anymore."

Richard Simmons disappearance

According to TMZ, Richard Simmons left the public eye amid health concerns. (Photo by Ray Tamarra/Getty Images)

In 2014, eight months after Simmons left the public eye, TMZ claimed that the star had "two bad knees." His operation on the first was so painful that he allegedly was delaying the second.

RICHARD SIMMONS SPEAKS OUT AMID SHOCKING DOC EXPLAINING HIS ABSENCE FROM THE SPOTLIGHT

In 2017, a woman alleging to have known Simmons for 35 years told the outlet that knee problems have kept Simmons in "virtual hiding."

The documentary claimed that Simmons delayed his second surgery because he was worried about being able to bounce back after the procedure and whether it would worsen any ailments.

Richard Simmons Katy Perry

Katy Perry and Richard Simmons attend the 2013 MTV Video Music Awards at the Barclays Center on Aug. 25, 2013 (Photo by Jeff Kravitz/FilmMagic for MTV)

"He wanted to be remembered as a vibrant, healthy man," the doc asserted, "not an elderly man with medical problems. Richard wanted to retreat before his image was recast as an old man. And his knee problems were a huge factor in his decision. He had a right knee replacement a few years back. And still needed a left one. He was in a lot of pain."

The special also alleged that there is one LAPD detective, who did not want to be identified, who has talked to Simmons over the years. According to him, Simmons "doesn’t want to be remembered as this frail, old guy. He wanted to be remembered as a guy that millions of people loved and watched. That’s why he disappeared."

FITNESS ICON DENISE AUSTIN, 65, AND DAUGHTER KATIE MODEL BIKINIS FOR SI SWIMSUIT RUNWAY SHOW: ‘PROUD MAMA’

Simmons was compared to Greta Garbo, the Oscar-nominated star of the 1930s who was fiercely protective of her privacy. She retired at age 35 and moved to New York City, where she led a private life until her death in 1990 at age 84. The special shared that "the Richard who disappeared is more authentically himself" than his "loud" persona.

Richard Simmons posing

Richard Simmons recently took to Facebook and thanked his fans for their support. (Photo by Harry Langdon/Getty Images)

"He has cleverly figured out ways to live in plain sight," it alleged. "He’s given up public life entirely… Richard is a master of disguise."

Still, Simmons has endured some heartache. Pals shared that his beloved eight Dalmatians have passed away over the years. His last dog died at age 17. Still, his housekeeper is "a fiercely loyal employee and friend."

A spokesperson for Simmons told Fox News Digital they had no comment about the allegations made in the doc.

‘30S STAR GRETA GARBO ‘HAD A VERY ACTIVE SOCIAL LIFE' AFTER LEAVING HOLLYWOOD BEHIND, GREAT-NEPHEW SAYS

Richard Simmons thanksgiving day parade

Richard Simmons attended the 87th annual Macy's Thanksgiving Day parade on Nov. 28, 2013, in New York City. In 2021, Fuse Sweat announced it would include Simmons' show in its line of programming. (Photo by Scott Roth/FilmMagic)

In 2021, Simmons revealed that he hoped a new generation of fans would be introduced to his classic exercise series, "Sweatin’ to the Oldies." At the time, it was announced that Fuse Sweat, a streaming channel, would include Simmons’ show in its line of programming.

"I am very excited that my groundbreaking fitness series of ‘Sweatin’ to the Oldies’ still is so relevant and popular and I hope many new fans will discover this timeless classic," he said in a statement.

“TMZ Investigates: What Really Happened to Richard Simmons" is available to stream for free on Tubi.