The 19-year-old tweeted the youngster after he sealed a move away from the Magpies.
Rolando Aarons (@R_Aarons16) September 1, 2015
Indeed, the duo were clearly close, often joking around together in training and on matchdays.
But it is Aarons who has made the greater first-team impact during his fledgling Newcastle career and Kemen has now been offloaded to Ligue 1.
It could be argued 19-year-old Aarons was preferred to Kemen and judged to have had greater potential, hence Newcastle's decision to sell the latter.
Either way, though, the young winger is sad to see his former team-mate go - a message that was reciprocated by Kemen on social media, too.
It was a quiet Deadline Day for the Magpies in the end, although Steve McClaren and co had promised just that.
It remains to be seen how Newcastle will respond in the January transfer window - and exactly how they will fare heading into that crucial point in the middle of the season.
McClaren's men are without a win so far this Premier League campaign but appear to be winning fans round by showing far more fight than they did under the hapless John Carver.