Sir Alex Ferguson and Arsene Wenger were bitter enemies for most of their time in the Premier League.
As Manchester United and Arsenal were battling it out for the title, the two managers personified the rivalry by coming to blows on more than one occasion.
But in Fergie's latter years at Old Trafford, the pair actually developed a mutual respect for each other and by the time the Scot retired in 2013, you could even go as far to say they became friends.
While Ferguson's United continue to struggle in his absence, Wenger has stubbornly remained at the Emirates.
This season more than any other, Arsenal supporters have frequently protested against the Frenchman's reign in charge, though.
Before the Gunners kick off their final league game of the season against Everton on Sunday, the club look unlikely to qualify for the Champions League for the first time in Wenger's reign.
And with his contract at the club expiring in the summer, there is a large portion of the club's fanbase who are praying Wenger leaves the club.
However, in a rare interview with the most successful manager in Premier League history, Ferguson has defended the Arsenal boss.
The ex-Man Utd boss has expressed sympathy towards Wenger and warned Arsenal fans to be careful about what they wish for.
"At the moment, of course, with the ridiculous situation of the pressure Arsene is under, I just wonder if they realise the job he's done," he told Sky Sports.
"The most amazing thing about him is this: he has come through a forest of criticism for months now, and has never bowed.
"He has seen it right through, he has shown a determination, a stubbornness. I think when you look at that, it's a quality, and I'm not sure they'll get another manager like that.
"It's quite easy to say 'Get rid of him', but who do you get? Who do you get in to keep that club the way they are for the next 20 years? I really feel sorry for him because I think he's shown outstanding qualities, and I think he has handled the whole situation. I don't know many that have done that.
He added: "Has long-termism vanished? I hope not, because I think the stability that a manager like Arsene Wenger has brought to Arsenal, and Brian Clough at Nottingham Forest, myself at United...there's no evidence that sacking a manager brings success."
It's hard to imagine Fergie heaping so much praise on Wenger when he first came to England over 20 years ago.
Wenger has been extremely coy over his future but is still expected to sign a new two-year deal at the Emirates.
And if, as expected, Arsenal are not in the Champions League next season it could be the most important campaign of his Gunners tenure.
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