The 44-year-old confessed she struggled to cope when Valentino was first diagnosed and that she felt as though she'd failed as a mother.
Presenter Mel received the news about Tino eight years ago and, according to The Sun, she said: "That was the first time I heard it and I didn't really know what it was.
"I had references like 'Rain Man', like we all do. I kept thinking, 'I hope he is deaf'. It's insane, when you think about it now.
"If I can't accept he's got autism I can't help him change."
Speaking at the London Autism Show, Mel read an extract from her diary which was written in 2007.
"I want to throw the towel in and wave a white flag. I desperately want to fold in my hand of cards.
"I've had enough – children, marriage, life, work, the lot, it's too hard to handle and I can't cope.
"I could cry until I dissolve, never to be seen again. I am so sick of failure that I feel, and overwhelmed by the future."
Mel is mother to Tino, 10, and 12-year-old Roman from her marriage to actor Daniel Caltagirone, who she split from in 2009.