It's fair to say Jose Mourinho and Arsene Wenger haven't always seen eye to eye.
The 'Special One' and the 'specialist in failure' have had numerous, well-documented squabbles since Mourinho arrived in English football in 2004.
The feud shows no signs of letting up now that the Portuguese boss has taken charge of Manchester United, though it may all come to an end if Wenger steps aside after this season's finale.
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It may surprise both managers to hear that they have more in common than they think. They're both Premier League winners - one rather more recently than the other, it has to be said - and they're both pioneers of the way their respective teams play football.
Petr Cech, who has played under both men, has also revealed one more trait that the pair share - they hate losing.
Speaking at a Guinness World Records event, brought to our attention by the Mirror, Cech has been looking back on his career, and he was quick to pinpoint the big similarity between Wenger and Mourinho.
"They are different but there is one thing they have in common, it's that they don't like defeat," he said.
"This is what is the driving force between the success of both of them.
Hungry for success
"You cannot last for such a long time if you don't have the commitment and the hunger and if you're doing everything to avoid defeat.
Cech, who has kept 181 clean sheets in the Premier League across his career with Arsenal and Chelsea, presumably doesn't like losing either, so it's a good job he's remained at the top for 12 years since arriving in England from French side Rennes.
While the 34-year-old has plenty to look back on, he also named the one save he remembers most - and it's the Arjen Robben penalty he saved in extra time in Chelsea's victorious Champions League final against Bayern Munich.
What was the biggest achievement - Wenger's Invincibles or Mourinho's Champions League win with Porto? Have your say in the comments.