Michael Cohen.
Washington CNN  — 

Attorney Robert Costello, once a legal adviser to Trump attorney Michael Cohen, will appear Monday before the New York grand jury investigating the former President Donald Trump’s alleged role in a scheme to pay hush money to adult film star Stormy Daniels.

Costello, who has represented Trump allies like Steve Bannon and Rudy Giuliani, told CNN he is appearing before the grand jury at the request of Trump’s legal team.

A person familiar with the matter told CNN that Costello contacted both the Manhattan District Attorney’s Office and lawyers for Trump to offer evidence that contradicts what Cohen has said publicly about the alleged hush money payments. When Cohen pleaded guilty to federal charges, he said he facilitated the payment in coordination with and at the direction of Trump.

CNN has reached out to the DA’s office.

While such a move is unusual for grand jury proceedings, the source told CNN that Trump’s legal team believes the district attorney is presenting the testimony for “optics.”

Cohen, a central figure in the grand jury investigation, said earlier Sunday that he has been asked to be at the District Attorney’s Office Monday as a rebuttal witness.

“Yes, I was asked to make myself available and to be at the DA’s office tomorrow as a rebuttal witness,” Cohen said on MSNBC Sunday. But Cohen had said he wasn’t sure if he’d be answering questions before the grand jury or in an interview with the Manhattan DA.

“Whether it’s before the grand jury or just with them for another interview, again, I’m not sure,” Cohen said.

The last-minute grand jury movement comes after Trump said Saturday he expects to be arrested in connection with the yearslong investigation into a hush money scheme involving Daniels, and called on his supporters to protest any such move.

In a social media post, Trump, referring to himself, said the “leading Republican candidate and former president of the United States will be arrested on Tuesday of next week” – though he did not say why he expects to be arrested. His legal team said after Trump’s post that it had not received any notifications from prosecutors.

Any indictment of the former president, who is running for the White House again in 2024, would mark a historic first and quickly change the political conversation around an already divisive figure. While Trump has an extensive history of civil litigation both before and after taking office, a criminal charge would represent a dramatic escalation of his legal woes as he works to recapture the White House.

This story has been updated with additional information.

CNN’s Kara Scannell contributed to this report.