The Dutchman, 66, is still furious that he was sacked on the Monday after his side beat Crystal Palace 2–1 at Wembley in May last year.
He was replaced in the Old Trafford hotseat by Jose Mourinho less than a week later.
Van Gaal has now broken his silence about the departure – claiming club officials were scheming behind his back.
He said: “They told me only after it was leaked out; it was the biggest disappointment of my life.
“United put my head in a noose and I was publicly placed on the gallows.
“I think it was all orchestrated like a film and it was done very much behind my back right from January.”
Manchester United eventually paid Van Gaal – who was two years into a three-year contract – £8.4million in compensation.
And Van Gaal added: “After what happened, I made them pay every penny.”