Quivers told listeners on Stern's SiriusXM radio show that her year-long leave of absence was the result of her battle with a rare form of cancer that started in her uterus.
But the good news? She says she's now cured of the disease.
"When it all was said and done, this had developed from endometrial tissue, which is uterine tissue, but endometriosis is when that uterine tissue grows outside of where it belongs," she told the shock jock (via TMZ). "And this is what had happened. There was endometrial tissue outside of where it belonged and the cancer developed from that."
As E! News reported back in May, 2012, the 61-year-old Quivers underwent major surgery to remove a very large tumor that had been pressing on her bladder and preventing her from going No. 1.
She disclosed the harrowing diagnosis after being asked by guest George Takei how her health was.
As it happened, the Star Trek vet was Stern's guest today when a caller asked when Quivers might be returning to the studio and Robin—who had been working from home and phoning in for the past 15 months since learning of her ailment—filled Howard and everyone else in on her condition after keeping mum for the duration of her illness.
In a summary posted by Stern fan site Mark's Friggin, Quivers said the operation lasted 12 hours and doctors found a grapefruit-sized tumor when they opened her up. They also warned her that depending on the situation, they might have to remove her colon and she'd have to live the rest of her life with a colostomy bag.
Luckily, things turned out for better and that wasn't necessary, though Stern admitted, "I gotta be honest. I thought she was a goner."
Robin added that after undergoing radiation and chemotherapy her physicians gave her a clean bill of health about three-and-a-half months ago and that she was now cancer free.
The King of All Media called Quivers' cancer "awful" and told listeners he would often end up in crying fits given what his close friend was going through.
Stern previously said after she announced her diagnosis the year before that he'd "kill" Robin if she got cancer and threatened to quit radio if Quivers wasn't there.