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Alexis Sanchez: Other sports stars who played for the enemy

With Alexis Sanchez now officially announced as Manchester United's new number 7, we've been taking a look at some other sports stars who joined their rival team.
"Keep your friends close and your enemies closer" - that's how the saying goes. Alexis Sanchez has clearly been paying attention, as he joins the Manchester United line-up from age-old rivals Arsenal.
Composite image showing Alexis Sanchez in Arsenal kit, and in his new kit for Manchester United.Getty Images
It's said that Henrikh Mkhitaryan initially didn't really want to leave United for Arsenal as part of the Sanchez swap deal, but after the deal was done he claimed 'it is a dream come true' to play for the Gunners.
Picture of Mkhitaryan in a United shirtGetty Images
And Sanchez is far from the first Arsenal player to swap the Emirates for Old Trafford. Arsenal fans were pretty cross when Robin van Persie made the transfer - and even more so when he helped his new team to take the 2013 Premier League title. Fuming!
Robin Van Persie holding his Manchester United shirt.John Peters/Getty Images
Sanchez and van Persie weren't the first top players to leave Arsenal fans crying into their red shirts. Ashley Cole ditched his team mates to join Chelsea back in 2006. He made the move to get more money, earning him the nickname "Cashley". Burn!
Ashley Cole playing for ChelseaLaurence Griffiths/Getty Images
It's not all been departures for Arsenal though. They managed to swipe Sol Campbell from their arch rivals, Tottenham Hotspur. The central defender had a long career at Spurs after moving up from their youth team. But he went from hero to zero when he ditched his long-time team to go and play at Highbury.
Sol Campbell playing for ArsenalIan Kington/Getty images
Transfer upsets don't just happen in football, and sporting rivalries don't come much bigger than the one between these two NBA teams. Karl Malone was a star player for the Utah Jazz, they've even got his statue outside their stadium. Karl ditched his team to join the Los Angeles Lakers, hoping to win his first NBA title. He got his punishment though when Lakers lost the finals and he ended his career without fulfilling his dream. What a shame!
Statue of Karl Malone outside the home of the Utah Jazz.Steve Dykes
When it comes to being punished though, this guy definitely comes off worst. Luis Figo's move from Spanish side Barcelona to rivals Real Madrid has been called the most treacherous transfer ever - and boy did he pay for it. Angry fans showed him what they thought of the move during a match between the two sides. When Figo came to take a corner right by his old team's supporters they threw a pig's head onto the pitch. Yes, that's right - a pig's head. Disgusting!
Luis Figo on the pitchChristophe Simon/Getty Images