Four-time major champion Kim Clijsters is set to come out of retirement and return to the WTA Tour in 2020. The 36-year-old Belgian, who retired after the 2012 US Open, announced the news on Thursday. 

"I don't really feel like I want to prove something," Clijsters said on the WTA Insider Podcast. "I think for me it's the challenge. 

"I have friends who would say, I want to run the New York Marathon before I turn 50. For me, I still love to play tennis. Whenever I'm at a Grand Slam playing the Legends, if somebody asked me hey, do you want to hit some balls, I'm the first one to be like I'll hit. I'll be the hitting partner for your practice today. I still love playing tennis. 

"The love for the sport is obviously still there. But the question still is, am I capable of bringing it to a level where I would like it to be at and where I want it to be at before I want to play at a high level of one of the best women's sports in the world. 

"I don't feel like I need to prove anything, but I want to challenge myself and I want to be strong again. This is my marathon. This is where I'm saying OK, let's try this."

Listen to Clijsters' full interview on the WTA Insider Podcast below: 

This marks the second time in the Belgian's illustrious career that she will return to the tour after an extended hiatus. Clijsters turned pro in 1997 and first reached No.1 in 2003. Two years after winning her first major at the 2005 US Open, Clijsters stunned the world when she announced her retirement at the age of 23 due to injuries and to start a family. 

Clijsters was back on the circuit two years later. In the interim, she gave birth to her daughter Jada in February of 2008, and she came out of retirement to play her first tournaments in August 2009 at the Western & Southern Open and Rogers Cup, immediately tallying two Top 10 wins.

Then, in just the third tournament of her comeback, Clijsters won the 2009 US Open as an unranked wildcard. En route to the title, Clijsters defeated Venus Williams, Li Na, Serena Williams, and Caroline Wozniacki to capture the second major title of her career and become the first mother win a major title since Evonne Goolagong Cawley in 1980.

Clijsters followed up her US Open title by adding five more titles in 2010, including the successful defense of the US Open. The Belgian won the third major of her comeback at the 2011 Australian Open and rose to No.1 a few weeks later, returning to the top spot for the first time since 2006.

Notoriously friendly, down-to-earth, and a favorite amongst her peers in the locker room, Clijsters hung up her racquet for good - or so she thought - after the 2012 US Open. In all, she amassed 41 singles titles in her career, including four majors, three WTA Finals titles (2002, 2003, 2010), and held the No.1 ranking for a total of 20 weeks. After retiring, she returned to Belgium with her husband Brian, gave Jada two younger brothers, continued her work at her tennis academy, and joined Eurosport as a commentator. 

In an interview on the WTA Insider Podcast, Clijsters said the idea of returning to the tour had been percolating for the last two years.

"Over the years I sometimes played with the idea but then I was like, No this is impossible," Clijsters said on the WTA Insider Podcast. "My life is here at home now and with the three kids, my youngest needs me the most. I couldn't see that being a part of my life."

But with her youngest son Blake set to start nursery, the impossible became more possible after a family trip to the Australian Open in January.

"That was the first time we were able to talk to our kids about how we were able to do that with Jada back in the day. I would talk to Jada and ask her, Jada, do you like this lifestyle? 'Yeah I love it!'"

Unable to shake her desire to return to the tour, Clijsters took advantage of the growing amount of free time on her hands with the kids now off to school. Working on her fitness became the perfect escape from the routine of "Mom Life". For the naturally gifted daughter of two top-flight athletes, putting her body through the fitness ringer became her self-care.

"Especially since the last birth, I worked out a bit here and there but it was nothing consistent going on. It was whenever I had time, between the kids and the Academy. Just balancing everything, I just didn't feel like I had the time to even just take proper care of myself."

"These last few months have been tough, but I feel like I've had more energy these last six months or so than I've had in the last two years because I'm taking care of myself better."

"These last few months have been tough, but I feel like I've had more energy these last six months or so than I've had in the last two years because I'm taking care of myself better. I'm not putting everything aside or towards the children, or I'm actually also giving myself some time, and it's something that I kind of forgot about a little bit, you know? 

"Even if I don't make it, this whole process has been so worth it for me to get back into a good routine. 

"I'm actually leaving the house in the morning after I've had breakfast," she said, laughing. "Like back in the day like with the three kids, I would sometimes just finish a little bit of oatmeal that Jada left in her bowl, or the kids left fruit out on the table that they didn't eat. That was my breakfast a lot of times because we were rushing to school, or I was being late to daycare." 

"Let's see if I can get my body in shape to play tennis at a level where I would like it to be at, that I have in mind of where I would like to get to, and see if it's possible. To see, first of all, if my body is capable of even doing that."

In the build-up to what will be her pre-season, Clijsters says her focus has been on fitness over tennis. Reunited with her fitness trainer, Sam Verslegers, she has seen her strength and flexibility increase and her reaction time, which she said was non-existent when she first began, has come back quickly.

"I love the challenge, I like to push myself," Clijsters said. "I'm surprised how, at times when I'm going through a rough practice, how easy it is for me to stick with it and to fight through it and to push through it. 

"It's a very satisfying feeling to have that kind of challenge again." 

Clijsters said the biggest concern surrounding her comeback is the effect on her three children, Jada (11), Jack (5), and Blake (2). 

"Of course, if you want to go through a marathon you're not going to have the whole media in your face," Clijsters said. "That was, to me, the toughest part about it. I know that I can handle it, but the kids, that's a different story. Our life is very easy and simple right now. It's not just my life that is going to change. 

"But then obviously I talked about it with my husband and with the team and then with Steve Simon from the WTA about being able to just hold off as much as possible to protect the children, obviously."

"Our life is so set when it comes to routines that our kids have, whether it's hobbies or schools. That's not going to change, I don't want that to change."

In order to accommodate her family, Clijsters says she will not play a heavy schedule and will remain flexible in her scheduling to accommodate any last-minute needs at home.  

"My head has to be clear for me to be able to leave the kids behind and to go to practice or to know that everything is organized at home and that dinner's ready for the next day or whatever it is you know that everything is planned," Clijsters said.

"Our life is so set when it comes to routines that our kids have, whether it's hobbies or schools. That's not going to change, I don't want that to change. I'm just going to be away a little more. If I feel like it's interfering with what's going on with the kids, then I'm not playing. Then I'll wait until it fits. 

"That's the great thing about the system that I didn't know existed. The fact that when you’ve been No.1, you've won a Grand Slam, and you want to come back then you can ask for wild cards.

"Starting off, you're not restricted to certain tournaments that you have to play. That's definitely a bonus, to hear that I don't have to play a set number of tournaments a year.
 
"So that, to me, was something that made the choice a little bit easier to take the step. If there would be a rule that said that you have to play a minimum number of tournaments a year then I would have said there's no way, I will never do that."

"There are times during the U.S. Open when I see some of the tennis I think, No way, that's not where I'm going to be able to get to because it just looks like they're hitting the ball so much harder."

Clijsters acknowledges that it's still a long road back to the tour. She has made great strides over the last months with her training, but the upcoming pre-season of tennis-specific work will test her body under more match-like conditions. 

Then come the actual matches.

In her position as a commentator and avid watcher, Clijsters has kept a close eye on the current state of the tour, which has seen unprecedented depth and a compelling clash of generations. She remains impressed by the power and athleticism she sees, but when asked what she expects as she moves from commentator to competitor, Clijsters grew pensive.

"I think for me to give an accurate answer to that I need to feel what it's like to stand across the net from these women," Clijsters said. "There are times during the U.S. Open when I see some of the tennis I think, No way, that's not where I'm going to be able to get to because it just looks like they're hitting the ball so much harder. 

"But I've always had that in me even when I was playing back in the day and when I was ranked up five in the world. I always saw everybody as, Oh my God, they move so well or they hit the ball so hard or they have so much variety in their game. And then when I stood across from them I felt OK. It actually doesn't feel as hard, the ball doesn't feel as powerful as when I saw it on TV or something. 

"I've always gone by feeling and emotion. I can't even remember how many times past players, current players, coaches have told me, What are you doing? You're still young enough, you should be competing with the best out there and I kind of always laughed it off. But I guess some of those words always kind of stayed in my head. But obviously not being in shape was obviously a big no or big question mark too, a thing that I had to handle before I could even think about doing something like this. 

"I feel like that is getting better and I still have time to become tennis-fit again. We'll see where it will end. But it's exciting and I'm happy with being able to do this and that, so far, it doesn't influence my life as a mother, as a wife. "I feel like so far it's only given me extra energy, and a challenge, a purpose. I've really enjoyed it. Maybe in a few months I'll regret it," Clijsters said, laughing.

For now, Clijsters is training with a January return in mind, but she is adamant that she has no desire to rush a return. She will come back when she is ready to go.

"We can talk about the start of 2020 and see where can we get a wildcard, but if I feel in December that I'm not even near to where I want to be, then I'm not going to go just for the sake of going somewhere. I want to feel like I'm getting to where I want to be. 

"I still have three and a half months before and so I still think I can have a lot of improvement to go through in these next few months and that I look forward to seeing where that will lead me."