Joe Manganiello "suffered in silence" as he battled a "deadly mystery illness" for almost a decade.
The True Blood actor has spent the past three years writing the memoir, Bloodlines, in which he chronicles his health battle, which involved "a cascade of autoimmune-related illnesses", chronic pain, and "a life-saving organ amputation", according to its publisher.
After the book and his secret health battle were revealed on Tuesday, the 49-year-old took to Instagram on Wednesday to share further insight into his fight with a "deadly mystery illness".
"For the better part of the past decade - most people don't know this - but I suffered in silence, battling a deadly mystery illness, and other than a very small circle of family and friends, I hid it from the rest of the world, and until recently hadn't really shared what I'd gone through," he told his followers.
Manganiello said that he sought the help of "the best doctors in the world", but they couldn't give him an explanation for what caused his illness.
"All their attempts to treat it with high-powered biological drugs only exacerbated my symptoms and then unlocked a host of brutal side effects that wound up plaguing me for years," Manganiello continued.
"And then in attempts to buy myself time, I underwent very serious operations and procedures that mutilated parts of my body and left me so weak at times that I couldn't stand up or walk."
The Magic Mike star added that he spent many months "heavily medicated" to try and cope with "excruciating bouts of chronic pain".
He explained that Bloodlines is a globe-trotting and time-jumping memoir that documents his 10-year search for answers and follows him as he makes some "absolutely unbelievable discoveries".
Manganiello concluded his video by saying, "If you're out there and you're suffering, then there's hope, and hopefully you'll get something out of it."
Bloodlines, published by Avid Reader Press, an imprint of Simon & Schuster, will be released on 13 October.
