Williams tells Britain's Daily Mail, "I knew I wouldn't be able to resist, eventually... Physically and vocally, everything about her is different from me.
"I've kind of gone to school and had teachers to help me understand Marilyn, so I could project an essence of her.
"When I first approached the part, I thought that there were three, even four parts to Marilyn. It rearranges you, it shifts your molecules, lifts you up, spins you around, puts you back down and you're not quite the same, for better or for worse."
And the blonde beauty insists her performance has brought her closer to the Some Like It Hot star, who died in 1962.
She adds, "I feel like we live together... At a certain point, something else does take over. I don't quite feel myself these days."