Donald Trump's daughter Ivanka has confirmed she was deposed this week as part of an investigation into her father's 2017 presidential inauguration.
The lawsuit in question, which is being run by Washington DC's Democratic Attorney-General Karl Racine, alleges funds from the inauguration were misused.
Specifically, it claims the inaugural committee "grossly overpaid" to use space at President Trump's hotel in the American capital.
In a post on social media today, Ivanka Trump called the investigation a "demonstration of vindictiveness" from prosecutors and a "waste of taxpayer dollars".
"This week I spent five plus hours in a deposition with the Democrat DC Attorney-General's office, where they questioned the rates charged by the Trump Hotel at the inauguration," Trump said.
"I shared with them an email from four years ago where I sent instructions to the hotel to charge 'a fair market rate', which the hotel then did.
"This 'inquiry' is another politically motivated demonstration of vindictiveness and waste of taxpayer dollars."
Trump included an image of an email, in which she said the hotel should charge "a fair market rate".
In the lawsuit, Racine alleges the Trump inaugural committee was fully aware that it was paying above-market prices to use the President's property, and did not consider cheaper options. He says there were more than a million dollars in "improper" payments.
One of the witnesses he cites is Stephanie Winston Wolkoff, a high profile event planner and former close friend of Melania Trump who has since had a very public falling out with the First Lady.
"She had concerns about the propriety of PIC (Presidential Inaugural Committee) holding events at the President-elect's own hotel and the excessive charges the Trump Hotel demanded for those events," court filings state.
"She expressed these concerns to President-elect Trump, Ivanka Trump, and PIC's deputy chairman Rick Gates, among others.
"Ms Wolkoff also contemporaneously documented her warning in an email to Gates and Ivanka Trump in December 2016 that the PIC was vastly overpaying for event space at the Trump Hotel.
"Ms Wolkoff asked them to 'please take into consideration that when this is audited it will become public knowledge that locations were also gifted and costs underwritten to lower rental fees'.
"The PIC and the Trump Hotel ignored these warnings and went ahead with the improper payments at issue in this case."
Wolkoff was friends with Melania Trump for about 15 years. The relationship with the First Lady deteriorated after she helped produce Donald Trump's US$107 million ($151 million) inauguration.
The event was dogged by allegations of funds being misused – there was a federal investigation into the matter long before the current one from Racine – and Wolkoff felt she was made a scapegoat for decisions made by the President and his staff.
She has since released one of many books about the Trump presidency, which is titled Melania and Me: The Rise and Fall of My Friendship with The First Lady.
The book was, in part, based on secret audio recordings of the First Lady, in which Melania criticised her husband and other members of the Trump family.
"Anybody who secretly tapes their self-described best friend is by definition dishonest," Trump's chief of staff, Stephanie Grisham, said in response to the book.
"The book is full of mistruths and paranoia, and clearly based on some imagined need for revenge."
Wolkoff's core grievance with the Trumps was that, in her telling, they failed to defend her when The New York Times reported her event planning firm had been paid more than US$26 million for its role in the inauguration.
In an interview she said that, in fact, only US$1.62 million went to her company.
When the controversy erupted, Trump said she had "no involvement" in the inaugural committee and "no knowledge of how funds were spent".
"When the time came for her to come and speak the truth about a friend who left everything behind to help her, she turned her back on me, stabbed me in the back," Wolkoff said.
"I gave Melania the benefit of the doubt that she was my friend, (that) she was different than Donald was, (that) she was different from the other Trump children.
"And now?" the interviewer asked.
"Oh, a Trump is a Trump is a Trump," she replied.
"The Melania I first met versus the Melania there is today is a very different person."