BBC: Kim Clijsters: Former world number one to return to tennis aged 36
Clijsters is targeting a return in January, but says she will remain flexible in her scheduling
Kim Clijsters is to make her tennis comeback at the age of 36 with a return to the WTA Tour in 2020.
The Belgian former world number one initially retired in 2007 to start a family, two years after winning her first Grand Slam at the US Open.
She returned in 2009 and won two more US Open titles and the Australian Open before her second retirement in 2012.
"I don't really feel like I want to prove something. I think for me it's the challenge," Clijsters said.
Speaking to the WTA Insaider Podcast, she added: "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 want to challenge myself and I want to be strong again. This is my marathon."
Clijsters is targeting a return in January, but says she will remain flexible in her scheduling.
As a former world number one, Clijsters is eligible for unlimited wildcards at WTA tournaments. She will need to play three tournaments or earn 10 ranking points to re-establish a ranking.
She said not having to play a set number of tournaments a year has "made the choice a little bit easier".
"Kim Clijsters ranks among the greats of the game and her return to the Tour is exciting news for the WTA family and tennis fans around the world," said WTA chairman Steve Simon.
Clijsters won 41 WTA titles and spent 20 weeks as world number one in her two previous spells.
Her daughter Jada was born in 2008, followed by sons Jack in 2013 and Blake in 2016.
Following her second retirement she ran her tennis academy and worked as a commentator, including for the BBC at Wimbledon.
She says she had been contemplating a comeback for two years.
"Even if I don't make it, this whole process has been so worth it for me to get back into a good routine," she said.
"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."
She added: "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."