Ambrose joined the club in 2003 from Ipswich Town during Sir Bobby Robson’s time as manager.
However, the midfielder was also a target for Arsenal, and he was set to “turn around” and speak to Arsene Wenger soon after arriving at St James’s Park for talks with Newcastle’s hierarchy.
Ambrose was only convinced that United was the right club for him after a late-night conversation with Sir Bobby which left him “stunned by his brilliance”.
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"To start with, I wasn’t actually going to sign for Newcastle,” Ambrose told the Racing Post. “My agent had been contacted by Arsenal – and I was going to turn around and go speak to them.
“He (Sir Bobby) was busy at the time, and he didn’t see me, so I was dealing with the chief executive and my Agent.
“In the evening I’d made my mind up – I wasn’t signed. I was going to go back to Ipswich, and I was going to talk to Arsenal. The door slams open, in comes Sir Bobby Robson, and I think we were there until 1am. I’d signed.
“By the time he left, I was stunned by his brilliance – he knew everything about me, about everyone. He told me about a game I played away at Grimsby, we lost 3-0 – the worst game I’ve probably ever played in my career – and he told me exactly every touch I had, and what I could have done differently.
“So, it was like ‘wow, if the guy is this committed to me, I want to be playing for him and Newcastle’.
“You look at the managers, and look at Jose Mourinho. He worked with Sir Bobby – and Sir Bobby taught him everything.
“He’s gone on to be one of the most successful managers, so it’s no coincidence that he’s worked with Sir Bobby, and, for me, he was by far the best manager I’ve ever played for – in terms of tactics and man management.
“He was just brilliant and there’s not many managers out there like that now.”
Ambrose joined Charlton Athletic in 2005 after finding his first-team opportunities limited at Newcastle.