The Twilight actor explained to the Daily Mirror: "I was at a small private school in London, I wasn't very academic.
"My dad said to me, 'OK, you might as well leave, since you're not working very hard'.
"When I told I him wanted to stay on for my A-levels, he said I'd have to pay my own fees, then he'd pay me back if I got good grades."
Rob put in the work and came out with an A and two Bs - but his father still didn't pay.
He added: "My dad told me a lot of stories. I would never buy a car from him."