Mouratoglou announced earlier this week that he would be working with Halep on a full-time basis.
He coached 23-time Grand Slam winner Williams since 2012, but the American star has not played since June after she injured her leg at Wimbledon.
In a statement on social media, Mouratoglou said he had missed coaching over the past eight months.
“I had a conversation with Serena, and the door opened for me, at least short term, to work with someone else,” he wrote.
In an interview with Tennis Majors, Mouratoglou disclosed more information about the chat with Williams.
“I missed it big time,” he said. “Coaching is the passion of my life. It’s the job of my life. And when I went to see Serena to discuss before starting with Simona, that’s what I told her.
“I said, ‘Coaching is the passion of my life and it’s difficult for me not to work.’ So yes, I missed coaching big, big time.
“Honestly, since I’m back to coaching with Simona, I cannot be happier to coach this again. It’s an incredible satisfaction for me to do that job. It’s incredible.”
Despite losing her coach, Williams suggested on social media she could return to action at Wimbledon, which is scheduled to run from June 27th to July 10th.
In a video posted on Instagram with Green Bay Packers quarterback Aaron Rodgers, Williams said: “I’m here with Aaron Rodgers and we’ve been talking about my comeback and he’s been hyping me up and getting me ready for Wimbledon.”
Rodgers then asks about the US Open, to which Serena replies: “Wimbledon is before the US Open. Exciting!
The Romanian now sits at world number 20, but Mouratoglou claimed he could oversee another rise to the top.
“I don’t think we should put any limits,” he said. “She’s been number one, she’s won Grand Slams. There is no reason why she couldn’t or she wouldn’t be able to do that again.
“So there won’t be any limits. The goal is not to say this is what we aim for, because sometimes you go even much further than what you think.
“The goal is to probably one day stop her career thinking, ‘I’ve done the maximum of what I could have done.’ And I think she has many years to go until she stops, and those many years, we want to make the best out of them.
“I think she has still such potential to improve in many aspects of her game. So it’s very exciting.”
