A former TV child actress who allegedly tried to undermine a venture fund co-founded by Silicon Valley billionaire Peter Thiel had something to hide — on her cellphone, the fund claims.

Crystal McKellar — who played Becky Slater on “The Wonder Years” before going on to become a Harvard-trained lawyer who worked at Thiel’s Mithril Capital — deleted nearly 2,000 text messages from her work phone before she finally gave it back to the fund last month, according to a new lawsuit.

The suit, filed by Mithril last week in Delaware Chancery Court, is the latest wrinkle in a bizarre case in which Mithril alleges that McKellar penned a series of inflammatory, anonymous, handwritten letters to its business partners — despite exiting the firm in February with a $225,000-a-year consulting gig, according to a suit filed this month in Texas state court.

“Shockingly, Ms. McKellar deleted nearly all of the text messages sent to or from her Mithril Capital Management cellular telephone, despite knowing that Mithril Capital Management was investigating her material breach of her agreements,” the Delaware suit contends.

A total of 1,941 text messages were sent or received by the phone in the eight months between McKellar’s February departure from the firm and the phone’s retrieval, according to court papers.

Yet the device itself contained only 32 undeleted messages when it was finally returned to Mithril on Sept. 30, according to the suit.

Mithril’s follow-up suit in Delaware court accuses 43-year-old McKellar of the “unauthorized removal, destruction, and attempted destruction of Mithril records and property.”

Reached by The Post for comment Tuesday, McKellar said Mithril’s fresh allegations were “news to me.” Previously, she told The Post she had done nothing wrong, and denied having “any anonymous interactions with investors.”

The earlier suit accused McKellar of mailing a series of anonymous letters that accused the fund of lying about the fees it was charging — allegations the fund denies. Mithril identified McKellar as the author after subjecting the letters to forensic handwriting analysis, according to the suit.

Mithril’s suit likewise claims that McKellar then attempted to lure its clients to other VC firms, telling some that Mithril was being investigated by US regulators. No federal investigation of Mithril has been confirmed.