On Monday, Grigor Dimitrov announced that he has split with his coach, Roger Rasheed.

Following a career-best season in which he won three titles, the world No. 11 has had a most challenging 2015, failing to reach any finals and most recently losing in the third round of Wimbledon. Last year, the Bulgarian reached the semifinals at Wimbledon.

“After much thought I have decided to end my working relationship with Roger,” Dimitrov wrote on Twitter.

Rasheed, who has also coached Lleyton Hewitt, Gael Monfils, and Jo-Wilfried Tsonga, began to work with Dimitrov in October 2013.

“After spending an exciting and successful period together Grigor has decided to end our relationship,” Rasheed said, also on Twitter. “I truly enjoyed our work and delivering my platform—I respect his decision and wish him nothing but success in his endeavors to achieve his goal in the world of upper echelon tennis.”