Cher filed a lawsuit against Mary Bono in Los Angeles on Wednesday, claiming Sonny Bono's fourth wife and widow is illegally withholding her royalties from Sonny & Cher's megahits in the '60s.

In court documents obtained by Fox News, the 75-year-old singer alleges the former member of Congress has breached a contract signed by Cher and her ex-husband after their divorce. Sonny, whose real name was Salvatore Bono, and Cher married in 1967 and skyrocketed to success as a musical duo. They split in 1974.

The documents cite a "1978 marriage settlement agreement" Sonny and Cher entered into after their split. Cher claims the exes "agreed to equal division of their community property."

"When they divorced, Plaintiff and Sonny agreed to an equal division of their community property and, to that end, in 1978 Sonny irrevocably assigned to Plaintiff, as her sole and separate property throughout the world and in perpetuity, fifty percent of their rights in musical composition royalties, record royalties, and other assets," the filing states.

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Sonny & Cher, 1965. (Chris Walter/WireImage)

It continues: "Since 1978, Plaintiff has been the unchallenged owner of her fifty percent of all musical composition and record royalties to which Plaintiff and Sonny were entitled by reason of their collaboration and marriage, including fifty percent of all royalties that Sonny, his businesses, and his successors, receive from those musical compositions and recordings."

It's been over 40 years since that agreement was established, and now, Cher's legal team claims Sonny's widow "claims that a wholly inapplicable statutory termination provision of the Copyright Act of 1976… has undone Plaintiff's ownership of her royalties from the songs and recordings that she and Sonny made famous during their marriage, and deprived Plaintiff of other long-established rights under the 1978 agreement."

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Sonny died in 1998 after a ski accident. Mary Bono was appointed the administrator of the late musician's estate shortly after.

According to the lawsuit, Cher formed The Veritas Trust in 1990, which is where her 50% ownership of the Royalties, would go. Although, she now claims, that "in or about 2016 the Heirs, or a majority of them, with the assistance or participation of Wixen, issued a notice of termination to various music publishers or other companies to whom Sonny had granted a transfer or license of the renewal copyrights, or rights under them, in the Musical Compositions. The Heirs’ notice specified various effective dates of termination ranging from dates in 2018 to 2026."

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The issuance of the termination was done "without" Cher's "knowledge or participation," the court papers allege.

Cher performs at Madison Square Garden on December 04, 2019 in New York City.  (Taylor Hil)

Sometime last month, representatives for the trust Mary manages also allegedly terminated "the stream of Composition Royalties that Sonny assigned to Plaintiff in the 1978 Marriage Settlement Agreement and, as a result, the Heirs' statutory termination ends her right to those Royalties."

Cher now claims Mary has refused to pay her and her trust the fifty percent of royalties she's owed and has repudiated her approval rights, among other issues. She claims the damages exceed $1 million and is seeking a trial by jury.

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Mary Bono did not immediately return Fox News' request for comment.