The Newcastle United man had some kind words for his former team-mate.
Many Newcastle fans felt the 19-year-old could have been given more of a chance at St James' Park but it wasn't to be and the teenager has now made his senior debut for Lyon.
Indeed, Kemen played Paris Saint-Germain of all teams - and Lyon beat the Ligue 1 leaders to end their unbeaten run.
And defender Mbabu sent Kemen a message on Twitter after his Lyon debut, congratulating him for his effort and had work.
Next up for Newcastle is a Premier League trip to Stoke City on Wednesday night and the Potters' 2-1 win against Aston Villa when not at their best was proof enough that Steve McClaren's men face a very tough test indeed - especially considering their away record.