It was a dream come true for the lank-haired Physics boffin and football fan - the chance to meet the players in the Barcelona dressing room before kick-off. But what should have been a friendly chat between Professor Brian Cox and Argentine striker Messi turned into a heated argument over the Falklands.
No-one quite knows what happened next, but it was Cox who donned the number 10 shirt and headed down the tunnel.
Cox: "I played out of my skin. I knew I had to, because I was wearing Messi's shirt, and he's the number one player in the world. But I was playing for Britain, not for Barcelona. I was playing for freedom and the people of the Falklands and all that is noble and great in the Universe, and on this wonderous, tiny, insignificant dot that we inhabit. So I gave it a right old go."
But no-one was more surprised by Cox's 5-goal tally than Cox himself. "Messi said he would get three when he went out there so I said I could get four. He said if I did he'd write to the President about the Malvinas. I'm looking forward to reading the letter now I got five."
"Thankfully we look pretty similar so no-one picked up on it during the game. Some people are still doubting it was me."