Is Dean McDermott a deadbeat dad?

That’s what his ex-wife is claiming in a pull-no-punches interview with the Daily Mail, alleging he told her he regretted the “terrible mistake” he made when he left her for current wife Tori Spelling.

In the bombshell interview, Mary Jo Eustace (former co-host of popular Canadian cooking show “What’s for Dinner?”) opens up about her legal battles with her ex, whom she’s taking to court (again!) over what she claims is $100,000 in unpaid child support for their son, Jack, now 19 and attending college.

Eustace and McDermott had been married for 13 years when he landed a starring role opposite Spelling in a made-for-TV movie “Mind Over Murder”. McDermott and Spelling became romantically involved, resulting in him leaving Eustace for the former “Beverly Hills, 90210” star. McDermott and Spelling were married in 2006; the couple is currently expecting their fifth child.

RELATED: Mary Jo Eustace Scores An ‘Absolute Win’ Against Ex-Husband Dean McDermott In Court

According to court documents obtained by Us Weekly, Eustace claims that McDermott has stopped paying child support while flaunting his lavish lifestyle. “Dean has stopped paying again,” reads Eustace’s most recent court filing. “In the last six weeks he has been on two luxurious vacations, Iceland and the Four Seasons in Punta Mita. He resides in a $2-million estate paid by his mother-in-law, Candy Spelling, and has no impetus to work. He owes over $100,000 moving forward, and I believe he has no intention of paying. He bounces my son’s university rent/tuition and is delinquent in paying therapist bills, while he shops visibly and throws lavish parties for his other five children.”

It’s that last item that Eustace says hit her son particularly hard. “When my son went to university, he didn’t get any financial support from his father,” she tells the Mail. “The one thing that his dad was going to do for him was pay his rent and he bounced his rent. It jeopardized his roommates and the apartment. One of the other dads had to cover the rent, so that really humiliated my son. I don’t even know if it’s paid back yet.”

Eustace, 55, reveals that isn’t even the worst of it. “My son has had his bank account cleaned out twice by debt collectors,” she says, citing her ex’s reported financial troubles.

RELATED: Default Judgement: Tori Spelling And Dean McDermott Ordered To Pay Bank $220,000 Over Unpaid Loan

In addition, she claims that McDermott, 50, made a shocking admission to her while visiting his son in Toronto.

“A year and a half ago, Dean confessed to me that he had made a mistake and he wondered what his life would be like if he had he stayed with me. He said, ‘Do I love Tori? Yeah. But I’ve thrown my life away,'” she alleges.

“We were on the street where we used to live. He fell to his knees crying, saying, ‘I can’t believe I gave this up.’ That is 150 per cent true. It was the most bizarre conversation ever,” she says, adding: “It made me feel irritated. I don’t want any more drama. It was crazy, extreme behaviour.”

Eustace filed a contempt of court charge against her ex back in March when he allegedly stopped making his $1,500-per-month child-support payments, but McDermott avoided jail when he and Eustace managed to come to an agreement.

However, she says she was forced to file another contempt charge against him October when he once again stopped making the agreed-upon payments.

RELATED: Did Tori And Dean Fake Affair For Publicity? McDermott’s Ex Thinks So

“When it stopped again, I said, it’s not even about the money anymore, it’s just about being respectful to my son and my family,” she says. “I wasn’t going to participate in a circus anymore, so I just took it into my own hands.”

Being hit with a second contempt charge, she says, could mean “jail time” for McDermott.

“People say, ‘Do you want him to go to jail? It’s not the intent behind this. It’s just to get him to honour his commitment,” she explains. “How could somebody not do everything in their power to avoid that situation?”

Adds Eustace: “It’s not up to me. It’s up to Dean to pay. It just seems like entitled behaviour… I’m disgusted and I’m humiliated. So many women go through this situation where they can’t get their child support and it profoundly affects their lives. So I was really strong about it and I just kept heading back into the courtroom.”

ET Canada has put in a request for comment from McDermott’s rep, but has yet to receive a response.