Fitness guru Richard Simmons has died, two law enforcement sources confirmed to NBC News.

Simmons was found unresponsive Saturday at his home in the Hollywood Hills of Los Angeles, one day after his 76th birthday, the law enforcement sources said. The exact cause of his death is pending.

Simmons’ brother, Lenny Simmons, confirmed the death in a statement.

“I don’t want people to be sad about my brother,” Lenny Simmons said. “I want them to remember him for the genuine joy and love he brought to people’s lives.”

“We are in shock,” Lenny Simmons added. “Please respect the family at this difficult time.”

Tom Estey, Simmons’ longtime publicist, said in a statement, “Today the World lost an Angel.”

On Friday, Simmons shared a message on social media thanking fans for the birthday wishes.

“Thank you…I never got so many messages about my birthday in my life!” Simmons wrote. “I am sitting here writing emails. Have a most beautiful rest of your Friday.”

He signed the post “Love, Richard.”

Simmons, the fitness coach known for his eccentric personality and “Sweatin’ to the Oldies” workout videos, rose to fame in the 1970s and 1980s after opening gyms and releasing dozens of fitness videos.

His website describes him as “one of the world’s most revered and iconic fitness personalities” who has been an “instructor and motivator for over 40 years.”

“By delivering a serious message with his trademark humor, he has helped millions of overweight men and women lose more than 3,000,000 pounds by adopting sensible, balanced eating programs and exercise regimes that are energetic, fun and motivating,” a biography for Simmons on his website reads.

Simmons grew up in New Orleans and struggled with his weight from a young age, weighing nearly 200 pounds when he was 15. By the time he graduated from high school, he was 268 pounds, according to his website.

He won a scholarship to study art in Florence, Italy, as a young man and, while eating outdoors, was approached by an agent who hired him to model for TV commercials. He ended up in more than 130 commercials, playing a range of parts, like a dancing meatball and a pat of margarine, and appearing in Fruit of the Loom underwear and with Dannon yogurt.

While at a supermarket one day, Simmons discovered a note stuck to the windshield of his Fiat that read “Fat people die young. Please don’t die.”

It prompted him to try anything possible to lose weight, including fasting, pills, exercise and injections. He dropped from 268 pounds to 156 pounds, but after several hair transplants and plastic surgery operations, he realized the importance of losing weight and getting healthy gradually, leading him to study health and nutrition.

From there, he took his talents to the West Coast in 1973, moving to Los Angeles, where he was unable to find a gym that “wasn’t for people who were already in shape,” according to his website. So, Simmons took it upon himself to create one, and SLIMMONS in Beverly Hills was opened in 1974.

While working as a maître d’ in Los Angeles, Simmons noticed what he believed was self-destructive eating behaviors of those he was serving, which led him to open Ruffage in 1975, a healthy restaurant with a salad bar, and the Anatomy Asylum, an adjoining exercise studio.

His concern for his patrons and his flamboyant personality attracted the likes of Barbra Streisand, Diana Ross, Dustin Hoffman, Paul Newman and Joanne Woodward. He also earned the attention of television producers who encouraged him to share his message and became a regular on TV talk shows.

It was at SLIMMONS where he taught classes and hosted seminars until 2013, his website said. His success also led to his own nationally syndicated series, “The Richard Simmons Show,” which ran for four years and earned multiple Emmy awards.

Simmons also released 65 fitness videos, which sold over 20 million copies, and wrote nine books and three cookbooks, according to his website.

Simmons had been something of a recluse since 2014, and in January, he spoke out against an upcoming biopic being made about his life starring actor and comedian Pauly Shore, which Simmons said he never permitted. 

“I have never given my permission for his movie. So don’t believe everything you read,” he wrote on Facebook at the time. “I no longer have a manager, and I no longer have a publicist. I just try to live a quiet life and be peaceful. Thank you for all your love and support.”

Since that post, Simmons has been active on social media, often writing motivational messages and sharing stories about moments and people in his life. The posts have ranged in topic from his childhood in New Orleans to racial segregation to fitness and his family.

He died just months after he posted a cryptic social media message, writing “I am ….dying.” He later walked it back, but the next day, he shared that he had been diagnosed with skin cancer.

In the March 18 social media post, he wrote that he had “news” to share.

“Please don’t be sad. I am ….dying. Oh I can see your faces now. The truth is we all are dying. Every day we live we are getting closer to our death,” Simmons wrote.

“Why am I telling you this? Because I want you to enjoy your life to the fullest every single day,” he continued in the post. “Get up in the morning and look at the sky… count your blessings and enjoy.”

The rest of the post included suggestions about how to lead a healthy lifestyle and reminders to hug the ones you love.

Later that day, he posted another update clarifying he was not dying.

“Sorry many of you have gotten upset about my message today. Even the press has gotten in touch with me. I am not dying,” he wrote. “It was a message about saying how we should embrace every day that we have.”

The next day, he shared that he had been diagnosed with basal cell carcinoma, a type of skin cancer.

The day after that, he shared in another social media post that the issue had been resolved after three procedures with a “cancer doctor,” Dr. Ralph A. Massey.

It was not immediately clear whether Simmons’ recent skin cancer diagnosis had anything to do with his death.