EXCLUSIVE: Richard Simmons' 'Only True Friend' Reveals Two Brutal Reasons Behind Fitness Guru's Mysterious Reclusiveness in His Final Years

Oliveira told us: "This was the true reason why he went recluse...the knee deterioration was just an aggravation to the situation."

Simmons quietly faded away from Hollywood back in February 2014 after spending decades in the spotlight growing his iconic fitness empire.

In late November 2014, rumors began circulating about why Simmons quit the spotlight.

In a statement at the time, he said: "I am so touched by the outpouring of love and concern I have received today.

"I have had a tough time dealing with this injury, as it is keeping me from doing what I truly love to do, and that is to teach classes around the world. Keep on sweatin'!"

Earlier this year, Simmons opened up about suffering a brutal injury in a rare social media post.

He explained his knee began hurting in 2009 after getting out of bed and then he proceeded to do all his leg stretches.

Simmons wrote: "When I taught my exercise classes, I would hear a little clicking in my right knee. I did not tell anyone about my pain. I couldn’t stand it anymore, so I had an MRI on my knee, and I was told I was bone-to-bone on my knee.

"(The doctor) told me there was not any cartilage. I asked him where did the cartilage go. He told me I had worn it out."

Simmons revealed that he went to the hospital to have stem cells removed from his back and "shot into" his knee — a technique called "PRP".

He wrote: "The doctor took the blood he removed and placed it into a machine that spins it. I waited an hour while this was being processed. The blood was injected back into my knee. This was a painful procedure. I did this on three separate occasions."