World number one Naomi Osaka has split from her coach Sascha Bajin.
The 21-year-old, who won the Australian Open last month and the US Open last year, announced on Monday that their successful partnership had come to an end.
No reasons were given.
Osaka tweeted: "Hey everyone, I will no longer be working together with Sascha. I thank him for his work and wish him all the best in the future."
Osaka enjoyed a remarkable rise up the world rankings after first linking up with Bajin in the 2017 off-season.
The Japanese player climbed from 72 to reach the top five during the course of 2018, when she won her first grand slam title, and then hit top spot after her success in Melbourne.
Bajin, who has previously worked as hitting partner for Serena Williams, Caroline Wozniacki, Sloane Stephens and Victoria Azarenka, was named WTA coach of the year in 2018.
He responded to Osaka's tweet by replying: "Thank you Naomi I wish you nothing but the best as well. What a ride that was. Thank you for letting me be part of this."