Peter Comfort, 90, met the Hollywood superstar to talk about his latest film Fury but admitted he had to use the search engine beforehand to find out who Brad was.
"Mr Pitt was very friendly and charming actually but I didn't know who he was," the World War Two veteran said.
"I said to him 'Until last night I didn't have a clue who you were and then I googled you and you've been in quite a lot of films'.
"They all rolled about laughing when I said that," he said after his trip to the Hertfordshire film set.
"I don't do modern films. I am a fan of actors like Alec Guinness, but of course he is dead now."
Peter, the last WW2 survivor of the 13/18th Royal Hussars, was signed up to the Sherman tanks at the age of 21. Brad wanted to ask him what life was like inside the tanks.
He landed at Sword beach on D-Day, 6 June 1944 on a day which saw 140 of his fellow soldiers killed and 350 more wounded.
The Fight Club actor plays the commander of a DD Sherman tank in his new WW2 thriller.
"My regiment, the Light Dragoons, got in contact with me about three weeks ago," Peter explained. "They'd been approached by an ex-officer who worked for a film company and asked if there were any old boys left.
"Then Brad Pitt phoned me and said he wanted to speak about Sherman tanks for a film.
"He talked me into going and, I have to say, I was extremely well treated. They wanted a lot of information to make it accurate and fired a lot of questions at me."
"Luckily there weren't any questions I didn't know the answer to," the grandfather-of-six said.
"The film crew got me up on the tank for a few pictures and wanted to know everything about it.
"They wanted to know where we slept, where we spent a penny, the living conditions and what it was like in action, so I told them.
"I don't like to talk about it because I saw too many people killed but Mr Pitt was very nice and I will be interested to see the film."
Peter has been invited to the British premiere of Fury which is expected to take place in November next year.