Their son Bear had just celebrated his first birthday when Liam Payne and Cheryl split in 2018.
Announcing their separation in joint statements, over the coming months and years, both gradually pulled back the veil to reveal what had gone so wrong.
Cheryl - who turns 39 today - explained that Liam's solo career after his split from One Direction was a big part of it.
Liam, 28, had dreamed of being a dad from the age of 16 and was determined to settle down and have a quiet life with Cheryl and Bear, five, but things didn't quite pan out that way.
"So he wanted to settle down and have a family and not do the solo thing," she told Sunday Times Magazine. "Then we encouraged him to do that. And then it didn't work out."
Admitting Liam may have felt somewhat excluded by her intense bond with the baby, when asked if Liam changed his mind about wanting domestic bliss, she responded, "You'll have to ask him that."
For Liam's part, he recently claimed that Bear's arrival 'ruined' their relationship, but for 'all the right reasons', and has said the first problems arose when the pressure of fatherhood knocked him for six.
"Becoming a dad at such a young age, it's such a difficult thing," he said in his documentary, Ant Middleton and Liam Payne: Straight Talking.
"And I think I built fatherhood up so much in my head that it kind of messed me up to start with. I started in a bad place with it," he continued.
"I think it spooked me out early on, and I was just worried I would not be enough to look after the both of them. They're so important to me - Cheryl as well."
The second issue, he said, was that he didn't "understand" what Cheryl was going through as a new mum.
"The one thing I was missing as a man in the relationship I had, was a level understanding about what she was feeling about stuff," he admitted.
"I think I learnt through away being that, while I want to protect her, there's a big part of her that wants to protect me."
Liam has recently been linked to his ex, Danielle Peazer, but has insisted that Cheryl remains the number one person in his life.
"She's one of the most, if not the most, important people in my life. I'm lucky I have someone who understands what I'm going through," he added.
Like Liam, Cheryl was just a teenager when she found fame on a reality show, winning a place in Girls Aloud on Popstars: The Rivals in 2002.
She first met Liam in 2008 when he was a 14-year-old hopeful on The X Factor and she was a judge. Their paths crossed again in 2015 when he returned to perform with One Direction and the rest is history.
Cheryl has credited Liam with being the only man not to have cheated on her. Like Liam, she harbours no ill will, insisting: "There's no animosity whatsoever. We are learning all the time. We're just like any other couple that have gone through this, but we have a few more eyes watching us... Just a few."
She told The Sun in 2019: “I’m actually really happy that we can be the way we are. We love and care about each other a lot and we share a child. It’s really important that we’re able to have a very healthy good relationship.”
She added: “We’re going to be in each other’s lives forever so we’ve got to figure it out and be grown-up about it.”
And Liam recently gave fans an insight into their co-parenting agreement. The exes live close to each other, and while Liam spends quality time with Bear, he says Cheryl gives him free rein to do what he wants.
"She is the best mum in the world. I couldn't ask for someone better," he told Logan Paul’s podcast Impaulsive.
"I get to take my son to school one or two times a week and it's the best thing. The relationship we have now as friends has only grown more.
"We broke up for a reason and now she gives me full autonomy of my life and to do what I do and I know he's [Bear's] taken care of. He is all she cares about and I couldn't ask for more. They live like three minutes from my house.
'I always glue myself to where he is. My life now is his. My money is his. He's a lovely, lovely boy. We've been blessed."
