Alex Ferguson and Arsene Wenger shared a legendary rivalry, constantly trading barbs and mind-games in the press and on the touchline. For a time, they were the greatest of enemies.
So Ferguson wouldn't have been happy to hear that, in the lead up to his much-touted retirement in 2001, Wenger was being targeted as his replacement.
It might have even been what convinced him to stay on.
According to former Manchester United chairman Martin Edwards, the Frenchman was the board's first choice to succeed Ferguson before he decided to continue in the job.
"Our first choice was Arsene," Edwards revealed in his new autobiography, Red Glory.
"Since joining Arsenal in 1996 Wenger had been greatly successful, especially in his first full season in charge when he won the Double.
"And while it's true to say he suffered hard times since, at the time we thought he was the best candidate to replace Alex. Certainly he was my number one choice.
He said that there was "a little bit of interest" from Wenger, who discussed the matter with Edwards and former chief executive Peter Kenyon.
"So we made our approach and Wenger did show a little bit of interest, enough to want to meet Peter Kenyon and me at his house in London to listen to what we had to say."
Several meetings took place, but Edwards thinks "loyalty" convinced Wenger to stay at Arsenal. In the following two years he won an F.A. Cup and went a season unbeaten in the Premier League.
"I think Wenger felt loyalty to David Dein," Edwards added. "He was very close to David and that was the reason he gave us in the end for turning down United."