It's 21 years since McClaren left United after his first successful spell at the club that saw them crowned treble champions soon after his arrival from Derby County.
And, in a recent interview with MiMentor, he remembered his first initial meeting with the manager, Sir Alex Ferguson.
He explained: "I said to him, 'what do you want me to coach?', and he said, 'I brought you here to coach, what did you coach at Derby? What you did at Derby, coach here."
McClaren, has made the same move again, landing at Old Trafford from a technical advisor role for the Rams, and United fans will be hoping for a similar impact when he links up with ten Hag, who was his assistant during his time as boss at Dutch side FC Twente.
McClaren also spoke to us about his career in the game that has taken him to clubs including Middlesbrough, Wolfsburg, Nottingham Forest and Newcastle, as well as a year in charge of the England national team.