President Donald Trump acknowledged paying off his personal lawyer – presumably for a payoff to porn star Stormy Daniels – through something relatively mundane: a mandatory financial disclosure filing.

The President said in his financial disclosure form, which was released by the the Office of Government Ethics on Wednesday, that he had incurred a debt to his longtime personal attorney Michael Cohen in 2016 – but he did not specify what that debt was for.

“In 2016, expenses were incurred by one of Donald J. Trump’s attorneys, Michael Cohen,” the form states. “Mr. Cohen sought reimbursement of those expenses and Mr. Trump fully reimbursed Mr. Cohen in 2017.”

Under the Ethics in Government Act, the President must include in his financial disclosure form any liabilities that exceed $10,000 from the previous calendar year. That would presumably include his $130,000 to Cohen, who he reimbursed for paying off Daniels, whose real name is Stephanie Clifford, in the weeks before the election to prevent her from discussing her alleged affair with Trump. Trump initially denied any knowledge of the payment to Cohen, but Trump lawyer Rudy Giuliani told the Wall Street Journal earlier this month that Trump had actually reimbursed Cohen for the payment in monthly installments of $35,000 throughout 2017.

The payment to Cohen was listed as a footnote under the liabilities section of Trump’s financial disclosure. The document emphasized that it was only listed for “transparency” and was not a necessity.

But in a letter to Deputy Attorney General Rod J. Rosenstein, David J. Apol, who is the acting director of the Office of Government Ethics, said it was requirement to report this payment – which experts say means that Trump could potentially have violated federal law if he knew about the payment last year and still omitted it from the report . This question is the subject of an amended complaint filed to OGE, the Department of Justice and the Southern District of New York. from the watchdog group Citizens for Responsibility and Ethics in Washington. Apol told Rosenstein he was submitting the letter in case it should be of use in “any inquiry you may be pursuing regarding the President’s prior report” from last year.

Trump has confirmed Cohen was paid through a “retainer,” but has not specified the timeline. But experts say that Trump’s acknowledgement means he not only has to disclose the payments on this year’s financial disclosure form, but explain why he left it off of last year’s, if he knew he had already incurred the debt.

“We know now based on the statements by the President’s own surrogates that there was this debt incurred in 2016, and still existed into 2017 – which is the relevant piece from this report. And it wasn’t disclosed last year, even though by all appearances it should have been,” said Adav Noti, senior director for the Campaign Legal Center. “So the question is not only will it be disclosed, and what explanation will be given for having not been disclosed previously?”

There was no explanation on the form for why it was not disclosed previously. The White House referred comment to Trump’s outside lawyers, who did not immediately respond to request for comment.

Noti also argued that the decision to dole out the money in monthly installments looks like a facade. “The payment was structured in such a way that you know you could draw an inference that not only was it not reported, but they’re attempting to conceal the payments,” said.

Daniels has sued both Trump and Cohen, the former for violating the non-disclosure agreement, alleging it was invalid because he didn’t actually sign it, and the latter for defamation.

Michael Avenatti, Daniels’ attorney said Wednesday that the acknowledgement of the payments will strengthen his client’s argument.

Mr. Trump stood aboard Air Force One on videotape and claimed he had no idea about the payment and now…as of this filing he had already reimbursed the payment in 2017,” he told TIME. “Theres no question this strengthens our case because it shows Mr. Trump knew of the agreement with my client and yet never signed the agreement.”

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Write to Alana Abramson at Alana.Abramson@time.com.