Early in 1669, he spent a month training with his French regiment in Lille. He had been appointed colonel of this regiment shortly before. This appointment made it even harder for others to believe he was not working directly for Louis XIV. However, Wilhelm was not above taking advantage of the French for personal gain. That July, he had his brother, Hermann Egon, arrange a meeting so that it would appear the Dutch were negotiating trade agreements with the League of the Rhine against France. This was done so that the French would give the brothers money that they would then use to purchase Mainau.