The former Guns' N' Roses guitarist walked in on his mother and the rock icon when he was eight years old.
Slash once caught his mum naked with David Bowie.
The former Guns N' Roses guitarist claims his late costume designer mother Ola Hudson shared a "mysterious romance" with the 'Ziggy Stardust' singer in the 70s and he once accidentally walked in on them together when he was a child.
Slash told Australian radio station Triple M: "He was always over - they were always together. I caught them naked once. They had a lot of stuff going on, but my perspective was limited.
"Looking back on it, I know exactly what was going on. When I look back on that whole combination of people, I can only imagine how freaky it was."
Rock icon Slash - who's parents separated in 1974 - added he didn't dwell on what he had seen until later on in life, when he realised his mother and David must have fallen for each other after working on a professional level.
Slash explained: "My mum started working with David professionally at first. I'm pretty sure that's how it started.
"Then it turned into some sort of mysterious romance that went on for a while after that.
"She did his wardrobe for his whole 'Thin White Duke' period and 'The Man Who Fell To Earth' movie that he did.
"She did all that and he was around for a while."
Slash will play a UK tour in October, beginning in Edinburgh on October 7.