The Jack & Sarah star was given a chance to grill Trump for his U.K. documentary series Hotel Secrets and he had just 10 minutes to chat to The Apprentice boss about his business empire.
Grant reveals he endured a stand-off with Trump when he threw in a question that hadn't been pre-approved by the businessman.
He tells Britain's The Independent Magazine, ""He changed the time of the interview about five times, he stipulated it must only be 10 questions in only 10 minutes, and he insisted on seeing all of the questions in advance... (I asked the first question and) he said, 'This isn't one of the questions I approved.' I said, 'Well I'm not (British TV interviewer) Michael Parkinson.' He asked me, 'Do you play golf?' I said, 'No, I don't play golf... because I was in the backseat of a car once and I saw my mother f**king my father's best friend and he was a golfer...' He said, 'Would you say this on live TV?' I said, 'Yeah, I'll say anything'.""
However, the encounter helped the actor as Trump warmed to him and let him continue the chat for an hour, even congratulating him on a job well done at the end.
Grant adds, ""From then on he was absolutely fine. He was there for an hour and, as he walked out, he said, 'You did a good job, kid.'""
The actor famously detailed the childhood trauma of seeing his mother with another man in his 2005 semi-autobiographical film Wah-Wah.