Lisa Marie Presley will testify against estranged husband Michael Lockwood in bitter divorce battle

Lisa Marie Presley and her estranged husband, Michael Lockwood, are gearing up for a showdown on Monday when their bitter divorce trial goes to court.

The couple split in 2016 after 10 years of marriage and Presley claims that the musician has since been trying to get a share of the inheritance left to her by her late father, rock 'n' roll legend Elvis Presley.

According to legal documents, the 50-year-old is set to take the stand to testify that her husband had "assured her that he was not that guy" after she told him before prior to their 2006 wedding that she "would not marry someone who would come after her for her money."

While Presley's fortune has dwindled in the years they've been married, she was once worth a staggering $87 million -- that's why one year after their wedding, she asked Lockwood to sign a post-nup for peace of mind. The post-nup was signed by both parties and stated that neither would pursue the other for support "at any time, regardless of the circumstances."

"So much for assurances," Presley's attorney, Gary Fishbein, said of Lockwood, who is now contesting the post-nup with Presley, the mother of his 9-year-old twin daughters, Finley and Harper.

Lockwood, 57, insists the document be void because he claims he was coerced into signing it, and his lawyer at the time -- who has since died -- failed to properly explain the terms of the agreement.

"Lockwood cannot now complain that he's sorry he entered the agreement because he doesn't like the terms," said Fishbein. "He knew what he was signing, was represented and cannot invalidate the agreement because he has a case of sour grapes."

Meanwhile, Presley has said in the court documents that she was $22 million in debt, with $14 million owed in back in taxes -- claims Lockwood refutes. In his filing, he claims that Presley earns around $5.8 million every year, or $480,000 a month, thanks to a trust set up by her  father.

The trial is expected to last four days.