Ian McKellen says the painful fall that sent him from a London theater to a hospital bed could have been way worse ... if not for his fat suit!!!
The legendary actor is recounting his nasty spill for the first time, telling Saga Magazine he fractured his wrist and chipped his vertebrae in the June incident ... but had his ribs spared by his costume.
As we reported ... Ian was playing John Falstaff in a West End production of "Player Kings" when he tumbled off the front of the stage during a fight scene and had to be rushed to the hospital.
Ian says he used a fat suit to play Falstaff and the extra cushion softened the landing when he fell ... saving his ribs and other joints in the process.
The 85-year-old says his neck and wrist are still not healed, and he doesn't leave his home these days just in case "someone bangs into me."
Ian says he got his foot caught in a chair on stage and as he tried to shake loose he kept slipping on other props and eventually landed on someone's lap in the front row!!!
IM also says he's replayed the fall in his mind countless times ... and he feels shame over the whole thing.