(CNN) Naomi Osaka has enjoyed a year of rare success -- ascending from world No.72 to top of the rankings with a pair of grand slam titles to boot.
The Japanese star's rapid rise would, on the surface at least, suggest a player-coach relationship in fine working order.
Yet 16 days after securing Australian Open glory against Petra Kvitova in Melbourne, the 21-year-old and her coach Sascha Bajin have announced a shock split. Few details have been released other than a short tweet apiece from the pair.
Osaka tweeted simply: "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."
Bajin responded in similar style, saying: "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."
The decision comes just months after Bajin spoke of his desire for his partnership with Osaka to continue in the long-term.
In an August interview with the WTA's official website, he said: "I believe in longevity and that if you work with someone for a longer period of time you can work more efficiently."
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Bajin, who had previously worked as a hitting partner to both Serena Williams and Caroline Wozniacki, was named as the inaugural WTA Coach of the Year at the end of 2018 -- his first year as a head coach.
The recognition was reward for a 12-month period that had seen Osaka claim a maiden major title at the US Open, as well as a first WTA Premier Mandatory win at the Indian Wells Open.
Her victory at Flushing Meadows was not without controversy however with Williams embroiled in a heated row with umpire Carlos Ramos that overshadowed Osaka's maiden grand slam title.
During Osaka's run at the US Open, she praised her German coach for a perceived calmness that has improved her game.
"He tries to make every day really fun and exciting," she said at a press conference. "For someone like me, that sort of thinks sometimes things are boring, that's good for me.
"I fight myself a lot, so he's sort of been, like, the peacemaker."
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In his WTA interview, Bajin was equally effusive in his admiration for Osaka and his role as a support for her.
"She's such a perfectionist that she just gets down on herself and is too hard to herself," he explained.
"So I have to be the contrast. If she's too negative and too down then I have to go and say it's OK. The world is round, the grass is green, everything is alright. But in general she is more hard on herself than she should be. She's doing her thing, she's doing great."
Bajin had arrived as Osaka's coach after she had chosen to split with David Taylor, the Australian who had also worked with Grand Slam winners Martina Hingis, Ana Ivanovic and Samantha Stosur.
The news means that all four current women's Grand Slam champions have parted company with their coaches within the last year.