Income-other: large yearly sum

I've tried searching an other thread on this but couldn't find any:

In income-other i recieve a large sum of money every year during the summer. It is not mentioned in my inbox or anywhere else where it comes from. It is around E 30 million. Could it have something to do with the chairman? Am i missing something obvious? I noticed it has dropped slightly over the years and now i'm worried it could someday go to 0. Im playing Feyenoord.

Anyone? Thanks.