"The problem was: at the time we had just parted company with (coach) Alexander Zorniger, that was just after the winter break in 2015. We didn't know at the time who would be our coach and how it would continue".
Rangnick added that Mbappe's father told him if he could assure him, "that I would be coach, that he would entrust me with the boy immediately. But in February  I could not give him that promise".
Meanwhile Mbappe secured a season-long loan move to Paris Saint-Germain this summer after netting 26 goals across all competitions for AS Monaco and has recently been nominated for the 2017 FIFA Ballon d'Or award.
Mbappe became one of the hottest properties in football last season, as he helped lead Monaco to the Ligue 1 title and the Champions League semi-finals, playing a starring role on both fronts.
The French side are now favourites to conquer Europe this season, and it's very likely that they will, having shown their intent by humbling Bayern Munich in a 3-0 defeat in their last Champions League match.