Brian Riemer has left Brentford as assistant manager to take charge of Anderlecht.
Riemer had been with the Bees for four years working alongside manager Thomas Frank.
"I'm very sorry Brian leaves us, but at the same time I'm very happy on his behalf, that he has been given a well-deserved opportunity to become a head coach in a top club with a great history in Belgium and all of Europe," said Frank.
"The ambition to become a head coach has grown with Brian in recent years, but he was extremely happy in Brentford and to be part of an exciting project here.
"He would not have left us for any job, and I wish him all the best of luck.
"I'm sorry to see him go, because he is a good friend and has been a big part of the success we have achieved in Brentford over the last four years, but when someone departs, it means a new dynamic begins."