WASHINGTON -- A top aide to President Trump announced Wednesday he's resigning. Staff secretary Rob Porter, who handled paperwork going to and from the president's desk, has been accused of abuse by two of his ex-wives. Porter says the accusations are false.

At first, the White House aggressively defended Porter, with chief of staff John Kelly calling him "a man of true integrity and honor." Press secretary Sarah Sanders said Porter "has been effective" and retained "the full confidence" of the president.

Kelly released a statement late Wednesday backing up his previous comment about Porter.

"I was shocked by the new allegations released today against Rob Porter," he told reporters. "There is no place for domestic violence in our society. I stand by my previous comments of the Rob Porter that I have come to know since becoming Chief of Staff, and believe every individual deserves the right to defend their reputation. I accepted his resignation earlier today, and will ensure a swift and orderly transition."

Despite the defense, everything collapsed as detailed allegations and documents emerged that depicted physical and verbal abuse allegedly suffered by two of Porter's ex-wives, Jennifer Willoughby and Colbie Holderness.

In a June 2010 statement to authorities in Arlington, Virginia, Willoughby said Porter punched the glass on their front door. "I called the police," she wrote. "I was afraid he would break in."

Willoughby wrote on Instagram in April 2017: "Just after our one-year anniversary, he pulled me, naked and dripping, from the shower to yell at me ... When I tried to get help, I was counseled to consider carefully how what I said might affect his career. And so I kept my mouth shut and stayed."

On Wednesday's press briefing, Sanders said Porter is "going to be leaving the White House."

"It won't be immediate," Sanders said. "He is resigning from the White House but is going to stay on to ensure that there is a smooth transition."

Porter called the allegations "outrageous" and "simply false."

As staff secretary, Porter was one of Mr. Trump's closest aides, acting as the conduit for all written information given to the president. Porter previously worked for Utah Republican Sen. Orrin Hatch.

Two sources with knowledge of the situation tell CBS News the FBI informed the White House in November about the domestic abuse allegations against Porter. It's unclear how the White House responded to this information.

White House communications director Hope Hicks, who CBS News has confirmed is dating Porter, played a significant role in drafting the statements by Kelly and Sanders in response to the allegations.