Aleksander “Sascha” Bajin was awarded the WTA Coach of the Year in 2018 after helping Naomi Osaka storm through a breakthrough season where she her first Grand Slam and shot from 72 in the world to fifth in the women’s rankings.

This is why the 21-year-old’s announcement that she had split from her coach Bajin on Tuesday, just 17 days after completing back-to-back Grand Slam victories at the Australian Open, sent shockwaves through tennis circles.

With no reason given and just a short tweet announcing the change gave rise to several questions. Eagle-eyed tennis fans pointed out that she hadn’t credited him as coach after her win in Melbourne and made several other comments which suggested that they were not in good terms.

“For me it’s a bit more – not that I’m ragging on Sascha, but it’s a bit more – it feels like I should listen to her more, in a way, because – oh, I’m going to get so much hate. You know, because I have seen what she did, and she’s also played. So it’s a little bit more believable,” Osaka had said about mentor Chris Evert.

This alluded to the fact that Bajin, a former player on the ATP Tour with a career high of 1149, hadn’t made his mark as a player. In fact, partnering Osaka was his first-full assignment as a coach. The 34-year-old had previously been a hitting partner for Serena Williams (2008-2015), Victoria Azarenka (2015-16), Sloane Stephens (2016) and Caroline Wozniacki (2017).

The duo joined forced late in 2017, after his last three assignments with ended briefly after an eight-year stint as Serena’s hitting partner during which she won 13 Grand Slam singles. Given that she is a big fan of Serena and the Williams sisters served as an influence at the start her tennis career along with her sister Mary, Bajin’s inclusion in her team seemed a crucial one.

Interestingly, Bajin had revealed in an interview that he was unsure about joining Osaka as coach after his last few stints ended early.

“I almost wanted not to travel anymore just because the last three times things ended a little bit too quick for me,” Bajin said. “I believe in longevity and that if you work with someone for a longer period of time you can work more efficiently. You know them better. It’s just a more intimate thing,” said Bajin.

“But then she’s such a sweet girl and the family was so kind and everybody embraced me and you know welcomed me, I was like I can’t turn it down. And I really saw big potential in her and I always wanted to figure out why she hasn’t been winning tournaments or competing and what I could maybe do to help her if I’m the one or not. So everything kind of worked out. Things happen for a reason,” had told WTA Insider in an interaction last August.

On her part, Osaka was all for continuing with Bajin in the last year.

Although this was his first time as coach, Bajin has enjoyed successful partnerships with the top players he has worked with. Serena won Australian Open (2009-10, 2015), Roland Garros (2013, 2015), Wimbledon (2009-10, 2012, 2015) and US Open (2008, 2012-14) as well as the singles and doubles gold medals at the 2012 London Olympics while Azarenka won three titles in 2016 (Brisbane, Miami and Indian Wells)

With Wozniacki, he was part of her team during one of her most consistent years as she won the WTA Finals and Japan as well as finishing runner-up at six tournaments, according to his profile on the WTA page.

While it is unknown where Bajin goes next, his services are sure to be in high demand given his credentials. He is currently headed home, adding on his Instagram page he was happy to travel even though the circumstances are not ideal.