The 32-year-old star and his former flame finalised their divorce last month after three months of arguing over their assets following their separation, and now Jack's mother Sharon, 65, has said she's upset the pair couldn't work out their differences, as she's always been a fan of Lisa.
Speaking on Howard Stern's 'The Stern Show' on Tuesday (04.09.18) morning, Sharon said: ''I'm sad. I'm very very sad. She's a good girl. And the thing is it just didn't work. They love each other [but] they can't live with each other.''
Lisa, 32, filed for divorce from the former 'Osbournes' star - with whom she has Pearl, six, Andy, three, and six-month-old Minnie - in May this year just weeks after the pair had split, citing ''irreconcilable differences''.
They couple wrote in a joint statement at the time: ''Hello! So the news about us separating has probably come as a bit of a shock to everyone. But, we just want to clear the air and share with you what's going on.
''So, first and foremost, we absolutely still love each other.
''Our family is the most important thing in our lives, and we tried everything we could for many years to make this work.
''What's best for our family right now is that we separate lovingly, and remain best friends who are committed to raising our children together.
''We had seven beautiful years of being a couple, filled with the most amazing moments and we will be eternally grateful to one another for that. We also have three wonderful children who we cherish more than anything.
''We are disappointed but feel confident that we will continue to grow our relationship as co-parents and best friends. Lots of love, Jack and Lisa. (sic)''
It was reported in August that they had settled the terms of their divorce, with Jack agreeing to pay Lisa a ''sizeable cash payout'' as well as cough up ''significant child support'' every month and cover school fees and medical costs.