Tottenham and Chelsea have one of the fiercest rivalries in the Premier League. In fact, behind Arsenal, there's probably not a club in England that Spurs hate more than the Blues.
The two sides both play in London, so there's already a basis for a local rivalry there. But adding the fact that in 2016, Chelsea ended Tottenham's title hopes at Stamford Bridge, the fixture has become even bigger recently.
Last season the pair were at it again, fighting it out to be crowned league champions. There wasn't a crunch fixture quite on the level of 'the Battle of the Bridge' that we saw in May 2016, but the rivalry still threatens to boil over every time the two teams step onto the pitch.
As a Tottenham or Chelsea player then, there are a number of things you should never do. You'd certainly be hated by one side's fanbase if you ever joined the other team.
In fact, even mentioning that you don't despise the opposite club would get you some funny looks from followers of your own team.
With that being said, Spurs youngster Georges-Kevin NKoudou has some explaining to do.
The 22-year-old has recently been pictured wearing a Chelsea training top. Yes, a Tottenham player has been seen wearing a Chelsea shirt.
If you don't believe it, proof can be found below.
Understandably, Spurs fans are not happy.
But the Frenchman has explained his reasoning for committing one of football's ultimate sins.
After being blissfully unaware of the storm he caused amongst Tottenham fans, for all of about five minutes, he quickly acted to defuse the situation.
The winger replied to a tweet questioning him wearing the shirt, saying:
"I'm wearing the shirt my friend @mbatshuayi gave me... NO disrespect here just old friendship sorry for not knowing."
So there we have it, it was all an innocent misunderstanding. NKoudou was politely wearing a shirt that Chelsea's title-winning hero Michy Batshuayi gave him.
As much as he feels that he's not in the wrong for wearing such a top, it's clear that the Spurs man will think twice before wearing it in public again.
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