The rugby player and The Saturdays singer ended their six-year marriage in 2018 after it was revealed that Ben had been unfaithful.
A year later in 2019 he wed American business woman Jackie Belanoff Smith after two weeks of dating on the day his divorce was finalised.
“Obviously, what I did was very selfish in regards to Una. I think it was a shock to her, me getting married so quickly,” he told OK! Magazine.
Speaking about the marriage he admitted he owes Una an apology for his behaviour.
“Una and I hadn’t been together for a year-and-a-half but I think what made it bad was it was such a big thing in the media and it was everywhere.”
“So, I did owe her an apology for that and should probably have let her know a bit more about what was going on”
Ben said that himself and his ex are in a good place now as they work together to co-parent their children Aoife-Belle (nine) and Tadgh (seven).
He is also father to Farrah (one) with new wife Jackie.
The former England rugby star admitted that moving to Ireland was another deal-breaker in his relationship with Una.
“It’s where she wanted to be. Coming towards the end of our relationship, we would talk about where we wanted to go and she wanted to go to Ireland but I never did."
“We had all these differences of opinion about life going forward. I think she’s very happy and she has found her place in Ireland. She’s such a good mum, too.”
Last week, Ben, who is set to star on ITV’s Dancing on Ice revealed how he told his kids about his split with their mother Una.
"I've sat down with the kids and talked to them about why mummy and daddy aren't together any more, so they have an understanding of it," he revealed.
"Obviously not massive details.”
“They are not stupid kids, they can read and stuff now, they are on social media,” he said.
“They talk to their mummy and they ask her difficult questions, and they ask me difficult questions, but we try and answer them as best as possible.”