Law enforcement sources tell TMZ … police and fire responded to a call from his housekeeper just before 10 AM Saturday and pronounced him dead at the scene. We’re told no foul play is suspected at this time, and cops are looking into it as a natural death.

Shockingly, RS posted multiple times on Facebook recently … including thanking fans for all the birthday wishes he received.

Simmons rose to fame in the 1970s and ’80s by opening a series of gyms including The Anatomy Asylum in Los Angeles. He released dozens of fitness tapes and DVDs including favorites like “Sweatin’ to the Oldies,” “Party off the Pounds,” “Blast Off” and many more.

Fans gravitated toward Richard for his positive, flamboyant energy … though in his later life he stepped away because of the demands of keeping up his persona in the spotlight — a topic we dove into in our documentary “TMZ Investigates: What Happened to Richard Simmons.”

We last caught up with Richard back in 2014 … and, he had a whole host of helpful hints for our viewers on how to get fit.

Richard was 76.

RIP