Kevin Costner and his estranged wife Christine Baumgartner are locked in a legal battle despite having an "ironclad" prenup.

Baumgartner, who first filed for divorce on May 1, is taking Costner to trial over the validity and enforceability of the premarital agreement the pair signed before their marriage in 2004. The two have also battled it out over custody and living arrangements with Baumgartner being forced to move out of the family home by July 31.

Celebrity divorce attorney Christopher C. Melcher explained to Fox News Digital the requests he's seen when it comes to prenups and which "clauses" can "threaten" the validity of the agreement.

"I have seen people ask for anti-cheating clauses to penalize a spouse for having an affair. There have also been requests that a spouse have sex on demand or maintain a certain weight to remain in compliance with the agreement," Melcher said. "None of these provisions are enforceable and should not be placed in an agreement because it violates public policy. Some have bragged about having these types of clauses in their agreement, but it threatens the validity of the entire agreement. It would be foolish to do so."

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photo illustration - Christine Baumgartner Costner smiles and looks toward her left and Kevin Costner in a white tuxedo looks semi-serious over a background of the Vanity Fair afterparty

Kevin Costner's estranged wife Christine Baumgartner was ordered to move out of the family home, owned by the actor, by July 31. (Lionel Hahn/Arturo Holmes/Karwai Tang)

"More sensible requests center around where their children will live or who will get custody in the event of a breakup," he added. "These are important considerations, but parties cannot agree on child custody in a premarital agreement."

There are things you can do to make sure your premarital agreement is enforceable, according to Marilyn Chinitz, a high-profile divorce attorney and partner in the matrimonial and family law practice at Blank Rome.

"In order to ensure that the prenuptial agreement is not at risk of being set aside, you must make sure that the agreement is fully negotiated, that both parties have counsel, and that full disclosure is provided as part of the agreement," she told Fox News Digital.

Christine Baumgartner walks in the courtyard of the court with her lawyer

Christine Baumgartner and her lawyer, Mark Rydell, leave court July 12, 2023. (Fox News Digital)

Christine Baumgartner stands in the doorway of the court with her lawyer

Christine Baumgartner will receive $129,755 in monthly child support from Kevin Costner. However, the two are due to go back to court over the number before the trial over the validity of the premarital agreement. (Fox News Digital)

The most unusual provision Chinitz has seen in a prenup required "a spouse to give the other spouse a foot massage once weekly. At first, I thought it was just injection of humor, but then found out it was not."

Despite legal advice not to put an anti-cheating clause in the prenup, a handful of celebrities have allegedly used this, including reality star Teresa Giudice. "The Real Housewives of New Jersey" star, who is now divorced from Joe Giudice, confirmed she had a premarital agreement with her ex during an episode of the show.

Joe and Teresa Giudice walking out of court

Teresa Giudice said she had a prenup with Joe Giudice. The couple divorced in 2020. (Getty Images)

"A week before we were getting married, Joe asked me to sign a prenup and I just felt when you love someone, you don’t do that," she revealed in 2020. "I didn’t even read it. I just said, ‘I want you to put one thing in there. If you ever cheat, the prenup is void.'"

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Jessica Biel and Justin Timberlake smiling at the Golden Globe Awards

Justin Timberlake and Jessica Biel allegedly have an anti-cheating clause in their premarital agreement. (George Pimentel/WireImage)

Justin Timberlake and Jessica Biel also allegedly have an infidelity clause. The agreement, which will divide up the couple's property if they ever divorce, holds Timberlake financially liable if he is unfaithful, the New York Daily News reported.

Melcher explained that there are cons to signing a premarital agreement, especially if resentment builds. "A one-sided agreement can make a spouse resentful," he explained. "I often hear, ‘I want our home to be our home, not yours.’ It doesn’t feel good to be told that you will get nothing in the event of a divorce."

However, celebrities such as Catherine Zeta-Jones, Khloé Kardashian and Jessica Simpson agree that the premarital agreement is important.

Zeta-Jones, who married Michael Douglas in 2000, fielded rumors about the couple's prenup for years. It was once reported that Douglas had offered to pay Zeta-Jones $1.4 million for every year the couple was married, in the event they got divorced, but that they settled on $2.8 million.

Catherine Zeta Jones and Michael Douglas at Golden Globes

Catherine Zeta-Jones previously said prenups are "brilliant" because everything is "sorted." (Dimitrios Kambouris/Getty Images for Hollywood Foreign Press Association)

"There was a load of rubbish written about it, but there was no arguing, no malicious feud," Zeta-Jones told Vanity Fair in 2001, brushing off the prenup rumors. "If I was marrying someone of lesser fortune who was 25 years younger, I’d be doing exactly the same thing. I think prenups are brilliant, because it’s all sorted out."

"Why should Michael be in a position where half of his fortune, which he’s worked bloody hard for, should land in someone else’s lap? It wasn’t a nasty experience for me; it was like, ‘Thank God that’s done – let’s get on with it!’ It was signed and put in the bottom of a drawer, hopefully never to be seen again. I get taken care of very well."

Carys Zeta Douglas, Michael Douglas and Catherine Zeta-Jones at Cannes

Carys Zeta Douglas, Michael Douglas and Catherine Zeta-Jones attend the 76th annual Cannes Film Festival on May 16, 2023, in France. (Vittorio Zunino Celotto)

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Melcher emphasized the money aspect of a premarital agreement while speaking to Fox News Digital.

"[A prenup] forces romantic partners to talk about money before they start their marriage. It is difficult to have conversations about ‘what if’ we break up or one of us dies during marriage, so they tend to ignore those important questions. Only after they are married do spouses learn each other’s financial expectations. A prenup negotiation gets all that into the open."

The divorce attorney added that some people might not marry after understanding their partner's financial expectations – like sharing property owned before the marriage equally, and more.

Lamar Odom and Khloé Kardashian pose for a photo

Khloé Kardashian noted the importance of a premarital agreement in 2011, while she was married to Lamar Odom. (Getty Images)

Kardashian, who was previously married to Lamar Odom from 2009 until 2016, also strongly backed the idea of a premarital agreement.

"Everybody needs a prenup!" the reality TV star told E! News in June 2011. "I mean, I don't care if you make $5 or $5 million, in this day and age... people are crazy, you never know. And when you have businesses together, like we do, you have to protect yourself. It doesn't mean you don't love them."

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Even Jessica Simpson, who did not sign a premarital agreement when marrying Nick Lachey, later regretted her decision.

"I wish I would have signed a prenup," she told Dr. Oz in 2020. "And that's the funny thing is that Nick wanted me to sign a prenup, but I was, like, so offended."

"I was like, ‘We're going to be together for the rest of our lives. We're saying our vows to God and in front of all of our family and friends. Like, this never gonna end.' And, we didn't sign a prenup."

Nick Lachey and Jessica Simpson attend an event

Jessica Simpson regretted not signing a prenup when she married Nick Lachey. (Getty Images)

Premarital agreements can be "tricky," but are a "major advantage" when it comes to keeping lives in order in the event of divorce, Chinitz explained to Fox News Digital.

Reasons for a premarital agreement "vary," according to Melcher, who says they can range from "a strong distrust that marriage can truly last a lifetime, to the need to control a partner, or simply good planning for the protection of both spouses."

"When someone has experienced divorce, whether as a child who witnessed a family breakup or from their own failed relationships, the fear of that happening again can motivate the person to want a premarital agreement. It is like making a new partner pay for the sins of someone else."

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