Carlos Alcaraz has split with his coach Juan Carlos Ferrero, the Spaniard said on Wednesday, ending a partnership that brought him six Grand Slam titles and world number one in the rankings.

Ferrero began coaching Alcaraz when he was 15 and guided him to several titles on the ATP Tour before he became a force to reckon with in Grand Slams, converting him from a claycourt specialist to a player who dominated on all surfaces.

“Thank you for turning childhood dreams into realities. We started this journey when I was barely a kid, and throughout all this time you’ve accompanied me on an incredible journey, on and off the court. And I’ve enjoyed every step of it so much with you,” Alcaraz wrote in a statement.

“We’ve managed to reach the top, and I feel that if our sports paths had to part ways, it had to be from up there. From the place we always worked toward and always aspired to reach.

Alcaraz finished the year with the French Open and U.S. Open titles while he won eight titles in all as he secured the year-end number one for a second time in his career.

He did not specify why he was splitting with Ferrero.

“Now times of change are coming for both of us, new adventures and new projects,” his statement added. “But I’m certain we’ll face them the right way, giving our best, as we’ve always done. Always adding up. I wish you all the best from the heart in everything that comes.”