A growing feud between Melania Trump and Hunter Biden intensified Thursday after the son of former President Joe Biden delivered an expletive-filled response to the first lady’s demand for an apology over a claim he made linking her to convicted sex trafficker Jeffrey Epstein.

In a YouTube interview last month with Andrew Callaghan, Hunter Biden alleged that Epstein — the financier and convicted sex offender who died by suicide in jail in 2019 — was the one who first introduced Melania to her future husband, Donald Trump. Melania’s attorney, Alejandro Brito, denounced the claim in a letter to Hunter Biden last week, calling it false and “extremely salacious.”

In a letter to Hunter Biden, first reported by Fox News, Brito threatened a $1 billion lawsuit if he did not retract the claim, asserting that it had caused Melania Trump “overwhelming financial and reputational harm.”

On Thursday, Hunter Biden returned to Callaghan’s YouTube program, where he was given the chance to apologize to the first lady.