One of Sir Alex Ferguson's biggest regrets at Manchester United must surely be selling Gerard Pique back to Barcelona in 2008.
The Spaniard arrived at Old Trafford in 2004 and despite showing huge potential was only afforded 13 senior appearances throughout a four-year spell.
Barcelona then returned for Pique by activating his €5 million buy-out clause, giving United no choice but to sell.
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And the rest is history. Since re-signing for the Catalonians, Pique has won six La Liga titles, the Champions League on three occasions and the Copa del Rey four times.
But perhaps there was another reason for United cashing in, because according to the Spain centre-back himself, he was a bit of a troublemaker at the Theatre of Dreams.
In an interview with TV3, Pique recalled the outrageous story of when he and his teammates made a bonfire in the dressing room and burned Patrice Evra's custom-made Nike trainers.
All in the name of banter, apparently...
"I'm a big fan of British humour," he said. "It was what I loved about Manchester. They don't get offended when you play tricks on them.
"They try to get you back, but they don't complain.
"Here at Barca, my humour hasn't always been appreciated by everyone. I deflate teammates' tires and other things, but this is nothing compared to what happened at United.
"One day Patrice Evra came in with shoes that he'd been asking Nike for months to make. They had the name of his children on them and all these crazy details.
"He went into the shower and we created a small bonfire and burned them. We recorded it and then sent him the video.
"In the first few years here [at Barcelona] I tried similar things but it didn’t work. It’s not the same culture.
"At United, they would take an expensive shirt that you have bought and put it on the free-kick mannequins. The shirt would be ruined because of all the mud it would get on it every time the ball hit it.
"It was a dressing room full of life."
Pique clearly found his 'prank' hilarious - I'm not so sure Evra would have felt the same.