 Complete the following phrase:  In May 2016, Frank de Boer announced that after 6 years and four domestic league titles, he would be leaving the club. Later in the month, it was announced that former Feyenoord technical director and player, Peter Bosz, would take over the side. After initially losing 52 on aggregate to Russian side FC Rostov in the Champions League qualifiers, Ajax would go on to play in the 