Sir Alex confesses: Henry's arrival at Arsenal turned my rivalry with Wenger toxic

What a rivalry, and what a clash of the titans it really was.

Sir Alex Ferguson and Arsene Wenger battled many times, and clashes between their sides, Man Utd and Arsenal, were much more than regular derbies during the late '90s and throughout the entire '00s.

There is a respect between the two managers even now - as demonstrated in Ferguson's appearance in a documentary about Wenger titled 'Arsene Wenger: Invincible'.

In it, the Scottish tactician spoke not only of Wenger's influence on English football as a coach but particularly the moves he made to compete with United - particularly with the signing of Henry.

Henry arrived at Arsenal in 1999 from Juventus, having struggled to make an impression as a winger. Wenger deployed him as a striker, and Henry hit new heights, scoring 175 Premier League goals in 258 games.

"It became toxic for a while, " Ferguson admitted via The Mirror.

"The big change that made Arsenal was reinventing [Thierry] Henry. And the goals… he was fantastic.

"You're always looking in the rear-view mirror to see who's coming up behind you, and when you see someone, you accelerate.

"Arsenal were catching us up, and their team was good enough to go above us. There's no question about that."

Ferguson won 13 league titles in his time as United manager, but even he still tips his hat to Wenger's side, going unbeaten across the 2003-04 season.

"I won 13 leagues, but I was never near going through a season undefeated," Ferguson told the documentary. "The achievement stands above everything else, and it was Arsene's."

Arsene Wenger: I should have left Arsenal way back in 2007

Ferguson stepped aside at United in 2013, with Wenger departing Arsenal in 2018.