Kevin Mbabu joined Newcastle United in 2013 following a successful trial, and spent four years with the Magpies.
The defender only made five first-team appearances during his time at Newcastle, however, with just three of those coming in the Premier League.
Mbabu spent time on loan at Rangers and Young Boys whilst at Newcastle, before joining the latter on a permanent deal in the summer of 2017.
The Swiss was outstanding for Young Boys last term, and was actually linked with a return to Newcastle during the recent summer transfer window.
Mbabu ultimately remained at his Swiss club, however, and helped them reach the group stage of the 2018-19 Champions League with victory over Dinamo Zagreb on Tuesday night.
The Newcastle fans have been reacting to the news on social media, and it would be fair to say that a number are still upset that their club allowed the 6ft ace to leave.
A selection of the Twitter reaction can be seen below:
Still for the life of me cannot understand why mbabu was sold.Awful decision.Sold for a pittance.
— Martin Williams (@Nitramantra) August 28, 2018
One of the biggest mistakes we’ve done is to let him leave, he would be perfect now as a backup for Yedlin and Dummett
— Adrian (@Adrian____29) August 28, 2018
Another young talent that didn’t get a chance at nufc.
— Gordon Wilson (@stangorwil) August 28, 2018
Newcastle really know how to buy and sell players…🤮
— Thomas Salvesen (@salvis205) August 28, 2018
Could not understand him being sold. Would have been so valuable now.
— Pete Clarke (@Peteclarke85) August 28, 2018
Aye another bizarre decision by Rafa to not keep this young man @Kevin_Baboo definitely should have been on our bench but he seems to be doing well at Young Boys – Congratulations Kevin 🙌🏼
— 🥅⚽ ▌▌▌Frankie ▌▌▌⚽🥅 (@franktastic9) August 29, 2018
Always a strange one why we let him go. Like santon.
— Craig Allen (@CraigAllenNCL) August 29, 2018