Anne Heche's son claims that a "will" presented by her former partner is invalid as it is not signed in the late actress’ handwriting.
Homer Laffoon, 20, filed a petition to control his mother’s estate earlier this month, following her death, which has been met with objections from James Tupper.
The youngster’s petition was made on the basis that the actress had died without a will.
Court documents show that though Tupper has yet to disclose his specific objections to Laffoon’s legal team, he has presented an email which he has referred to as a "will".
Lawyers for the 20-year-old say the email in question "fails to satisfy the legal requirements" for a valid holographic will.
"Mr Tupper repeatedly refers to the email attached to the Objection as a 'will,'" the documents, filed as a supplement to Laffoon’s original petition, state.
"However, as a matter of law, the email does not qualify as either a holographic will or formal witnessed will.
"The email fails to satisfy the legal requirements for a valid holographic will because the material provisions of the purported will are not in the handwriting of the Decedent.
"The email fails to satisfy the legal requirements for a valid formal witnessed will because the email was not signed by the Decedent and does not have two witnesses who signed the document during the lifetime of the Decedent."
The filing also claims that Tupper has made "personal attacks" on Laffoon ahead of a hearing on 11 October to further determine the administration of Heche’s estate.
The actress was involved in a serious car accident in Los Angeles on August 5, in which her vehicle collided with a building and burst into flames.
She was declared brain dead on 11 August and was kept alive on life support for three more days so her organs could be donated.
Heche, 53, was among the biggest film stars of the late 1990s, starring opposite actors including Johnny Depp and Harrison Ford, and had worked consistently in movies and television for more than three decades.
She was the former partner of US talk show host Ellen DeGeneres – the pair began dating in 1997 before separating in 2000.
Heche later suggested their public relationship had led to her being blacklisted professionally, describing herself as "patient zero in cancel culture".
She was married to Coleman Laffoon, a television camera operator, from 2001 to 2009, and was in a relationship with actor Tupper from 2007 to 2018.
She had a son with each man.
Source: Press Association