Arsenal legend Patrick Vieira has revealed he started the infamous tunnel row at Highbury in 2005.
Vieira, who was Gunner's midfield backbone, sparked a hostile exchange of words between the two bitter rivals when the players lined up in the tunnel ahead of kick-off.
And the bust-up, which was partially captured by television cameras, displayed an angry Roy Keane responding violently to Vieira after he exchanged words with United defender Gary Neville.
United went on to win the Premier League clash 4-2 and neither side was punished for the incident.
And now, the former France star Vieira admitted he caused the tunnel chaos in an ITV documentary, Keane and Vieira: The Best of Enemies, to be screened on Tuesday.
"I started it," Vieira said. "I was cool, I was really calm, I was smiling at him - and then he lost it.
"When we played at Old Trafford his (Gary Neville's) tackling was flying in on Robert Pires and he was doing it on purpose, and I said 'listen, we are not at Old Trafford here, this is Highbury'.
"So I said to him 'if you touch Robert, I will come after you'."
Meanwhile, Vieira also believes his former club has a problem - which is the lack of leadership; and this could ruin their bid to end their trophy drought.
"I think when you look at Arsenal they play fantastic football, but you need to win games playing badly and I don't think Arsenal are capable of that at the moment," Vieira said.
"And maybe as well there is a lack of leadership. They may not have a Tony Adams, a Sol Campbell, a Martin Keown.
"These kinds of players who can be a leader on and off the field."
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