A wealthy technology investor who also works as a DJ says she is preparing a defamation lawsuit against her former girlfriend, a television actress, after a series of explosive allegations surfaced during their breakup, according to court documents.
Lucy Guo, 32, an AI entrepreneur once described as the world’s youngest self-made female billionaire, told a federal court that she intended to take legal action against British actress Wallis Day, also 32.
The bitter end to their relationship was outlined in a petition filed by Guo in the United States District Court for the Northern District of California. The application seeks permission to subpoena Meta, the parent company of Instagram, for information about a post allegedly shared by Day.
Guo is seeking details about how widely the Instagram content circulated. In her declaration, she described Day’s post as defamatory and said she planned to pursue a claim in the UK.
The filing said Guo had uploaded an Instagram story promoting her latest single and remix, “Done with your ex.” The post reportedly included the caption: “fun fact: I broke up with my ex the night we made this”.
Day, who appeared in the CW series Batwoman and has about 425,000 followers, allegedly reposted the message with a caption accusing Guo of trying to make her sign a prenup, arriving intoxicated and attempting to have sex after she had refused, and taking hundreds of thousands of dollars’ worth of her belongings in an effort to pressure her into signing a nondisclosure agreement.
According to the court papers, Day’s post went on to accuse Guo of being “dangerous” and alleged that she had once prevented emergency responders from entering her home while someone was dying because drugs were present. The message also included the hashtag “#narcissist.”
Guo rejected the allegations, calling the Instagram story “replete with falsehoods.” In a statement to the Daily Mail, she said: “I categorically deny these allegations. They are false, deeply damaging, and do not reflect what occurred.”
Lucy Guo, a 32-year-old AI entrepreneur once described as the world’s youngest self-made female billionaire, says court filings show she plans to take legal action against her former girlfriend
Wallis Day, known for her role in the CW series Batwoman, is accused in court papers of sharing a defamatory Instagram post with her 425,000 followers
The filings include what appears to be a screenshot of a post Guo says Day shared after their relationship ended. Guo denies the allegations and says the post forms the basis of a planned defamation case
“My legal team is addressing this matter through the appropriate channels, and I intend to vigorously defend my reputation,” Guo continued. “Any suggestion that the current US proceedings are irrelevant is misplaced; they are a legitimate and necessary means of obtaining information directly relevant to the intended UK claim.”
The Daily Mail has contacted Day for comment. A Meta spokesperson said the company’s 49 percent stake in Scale AI would not influence how it responds to the request, adding: “Meta discloses account records solely in accordance with our terms of service and applicable law.”
Guo, whose fortune Forbes estimates at $1.5 billion, described the allegation involving emergency services as the “most offensive statement,” insisting it was completely untrue.
“I never refused to let emergency services into my house to help anyone, let alone when someone was dying,” she said in the declaration.
The planned legal action follows what Guo characterizes as a particularly acrimonious breakup.
The court documents state that Guo and Day began dating in July 2025, with Guo ending the relationship in February 2026.
“Thereafter, Day sought, unsuccessfully, to obtain hundreds of thousands of dollars from me,” Guo alleged in the filing.
Guo wants access to a digital record from Meta that could help determine the potential scale of any damages if a court eventually rules in her favor.
The proposed subpoena seeks 18 categories of information from Meta, including the identities and locations of people who viewed Day’s Instagram story
Guo is also asking Meta to disclose when the post was uploaded and removed, who could access it and how many times it was viewed
Forbes values Guo’s fortune at $1.5 billion, with much of her wealth tied to her stake in Scale AI, the data company she co-founded
The subpoena request covers the timing of the story, its audience and the number of views, likes, shares and reposts it received.
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Guo is also seeking information showing how many followers each woman had before and after the post was published.
That geographic data could prove significant if Guo brings her case in Britain. Under UK defamation law, the number and location of people who saw an allegedly defamatory statement can help establish whether it caused serious reputational harm.
The filing again requests data on the follower totals of both women before and after the publication.
Guo submitted the application ex parte, meaning a judge may review it without Day’s lawyers present to challenge the request.
The move has prompted questions from legal observers because both women already have legal representation and have been corresponding about the dispute.
Eric Goldman, a law professor at Santa Clara University, said Day’s lawyers could be caught off guard by the application.
“Doing an ex parte proceeding when you know the other side has lawyers involved is just not great,” he said. “It might be proper, but it still is uncomfortable.”
Guo grew up in Fremont, California, taught herself programming as a child and later left Carnegie Mellon University after receiving a $100,000 Peter Thiel fellowship
Day studied at the Sylvia Young Theatre School and the Arts Educational Schools in London before appearing in productions including the DC Comics series Krypton
A committed nightlife fan, Guo has said she sees no conflict in being a CEO, investor and DJ who continues performing until 2am
Goldman said that without opposing lawyers present to argue that the request was overly broad, a judge might “just gloss over” the extent of the information being sought.
Guo’s attorneys at Los Angeles firm Kinsella Holley Iser Kump Steinsapir have characterized the requests as narrowly focused.
The case also highlights the contrasting standards for defamation claims in the United States and the United Kingdom.
As a public figure in the US, Guo would generally need to show that Day acted with “actual malice” — either knowing the statements were false or publishing them with reckless disregard for whether they were true.
UK law is generally more claimant-friendly in this area. If a defendant relies on the statutory defense of truth, they typically must prove that the allegedly defamatory statements were substantially true.
Guo has retained prominent British solicitor Paul Tweed, who says he has worked on several hundred high-profile defamation cases.
At the time of the US filing, no substantive defamation lawsuit had been lodged in Britain.
The dispute is the latest dramatic chapter in Guo’s unconventional rise through Silicon Valley.
Raised in Fremont, California, she learned to code as a child before leaving Carnegie Mellon University to accept a $100,000 fellowship from Peter Thiel. She later became Snapchat’s first female designer and co-founded Scale AI in 2016, a company that helps clients label and organize raw data.
After departing Scale AI two years later, Guo retained a stake that ultimately became the foundation of her vast fortune.
Despite her wealth, Guo has never closely followed the traditional image of a Silicon Valley executive.
An avid runner and enthusiastic participant in nightlife, she once told Out magazine: “You can be a CEO and an investor and DJ until 2am. You can care deeply about your work and still have a huge, weird, fun life outside of it.”