Simona Halep and longtime coach Darren Cahill have agreed to end their successful six-year partnership. The former No.1 and two-time major champion announced the news on social media. 

"After six wonderful years working together, @darren_cahill and I have decided that it's time to end our working relationship," Halep wrote on Twitter. "Thank you D for everything, for making me a better tennis player and a better person."

Coming off a breakout 2014 season in which Halep made her first major final at Roland Garros as well as a Wimbledon semifinal and Australian Open quarterfinal, Halep and Cahill joined forces for the first time in the summer of 2015. At the time, the Halep was a solid Top 5 player who was still chasing two significant milestones - break through to win her first Slam and become the first Romanian woman to be secure the No.1 ranking - and Cahill was part of the Adidas Player Development program. When Adidas shuttered the program permanently in the fall, Cahill transitioned to become Halep's full-time coach.

Under Cahill's tutelage, Halep would embrace not only the evolution of her game but also her mental strength. An ambitious, self-critical and fiery personality at the beginning of her career, with Cahill's guidance and encouragement, Halep began to take a more holistic, kinder approach to herself and her tennis.

Slowly, Halep began to phase out the negativity that would unwind her during matches. After a famous on-court coaching timeout during the 2017 Miami Open frustrated Cahill, the Aussie abruptly quit his post in hopes of shocking Halep into accelerating her transformation. The gambit proved successful and the duo reunited ahead of Roland Garros that year.

Halep would bounce back from a heartbreaking loss in the 2017 French Open final to Jelena Ostapenko by finally crossing one item off her to-do list: to become the WTA World No.1. Halep achieved the feat at the China Open that fall and finished the year as the 13th year-end No.1 in WTA history and the first Romanian to hold the top spot. 

As Halep continued to be the most consistent top player on tour - her long-ranging stint inside the Top 10 lasted for 373 straight weeks - she finally got her hands on the trophy she desperately wanted. In 2018, she came through in her fourth major final and third at Roland Garros to defeat Sloane Stephens and capture the Coupe Suzanne Lenglen.

Less than a year later, Halep would stun the tennis world with a dominating performance at Wimbledon to win her second major title. Cahill was not in the coaching box for her Centre Court performance, as the two agreed to take a break in 2019. But Cahill was never more than a text or phone call away, offering advice and support before formally reuniting in 2020. 

Throughout it all, Halep has been the first to credit Cahill for not only her evolution into one of the best players of her generation but also her development as a person off the court.

"He told me a few days ago, that when we started you were No.2. I said, Yeah, but from No.2 to No.1, it's a long way."

- Simona Halep

Here are five quotes that illustrate how foundational the Halep-Cahill coaching combo over the past six years:

Halep at 2016 Wuhan: "He doesn't think that it's a big deal if you change something. He shows me it's not a big deal if I change something. So now I'm more relaxed to change things and I'm more relaxed to try to do better. Even if the next day is not going to work as I want, maybe in the future is going to work how we want, how we wish.

"Yeah, now it's much easier for me to change things. It is much easier to listen, to accept things that I have to change and just going forward."

Halep at 2017 Madrid: "He knows how to calm me down. I just try to learn how to relax myself and how to be dedicated to this sport, not to the result. I'm doing what I love, so I have to put the desire into the positive things on court. I'm trying that. I'm working on that. I feel that I'm a much better player since I worked with him.

"I hope to make him prouder winning a Grand Slam in this career."

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Halep at 2018 Roland Garros: "In my opinion, he made everything to me to be able to get the No.1 seed. He told me a few days ago, that when we started you were No.2. I said, 'Yeah, but from No.2 to No.1, it's a long way.'

"So I think because of him, and his personality, he's very relaxed, he's Australian, so has to be like that, very relaxed, very open, he made me be the same and to embrace more the pressure, the emotions, and to understand myself better.

"That's why I was able to have great results and to get to No.1. He's a great person and the best coach."

Chris Evert at the 2019 WTA Finals: "The coaches, they really play a big part in today's game, bigger than we think. I think Darren had a lot to do with it. The fact that he left her after Miami because her temperament wasn't good. She was so tough on herself and she was hard on herself and hard on her team on the side.

"He was like hitting his head in the wall trying to get her to calm down and not be so feisty out there. I think when he left he said, 'You know, you're not doing what I'm asking you to do and you're not being fair on yourself or on your team. You've got to change.' And he left.

"I think that opened her eyes to, you know, I better be more professional on the court. I better have more belief in myself. I better manage myself emotionally a lot better.

"As soon as she turned the corner there, I think her whole game changed. I mean, she won matches when she was down; whereas before she would be - I saw her a couple of matches she'd be down a set and a break and she'd start slashing balls and not really caring if they are going in the fence or in. She started to still hang in there when she was losing and not get upset. That turned her whole career around."

Cahill at 2020 Australian Open: "We would speak most days, even last year when we weren't working together [in 2019]. We're friends. As I have said many times before, she's really a part of my family.

"I told that story about thinking I was doing the right thing for my family over 12 months ago when I came home and said, 'Hey, kids, I'm taking a year off work and I'm going to be around a little bit more,' and my daughter started crying. I thought she was really happy but she was pissed that I was leaving Simona. That's what she means to my family."

Darren Cahill reflects on his time coaching Simona Halep