Jerry Falwell Jr has announced his resignation as head of evangelical Liberty University amid conflicting claims about a sexual relationship his wife had with a younger business partner.

Mr Falwell confirmed his departure to the Associated Press a day after the school said he had submitted, then rescinded his resignation.

He exit marks a precipitous fall from power for a once towering force in the US evangelical Christian movement whose endorsement played a key role in President Donald Trump’s 2016 victory. The Lynchburg, Virginia, university was founded by Falwell’s late father. His son became head in 2007.

According to the school, he initially offered to resign on Monday, hours after Reuters published an interview with a man who said he had had a years-long sexual relationship with Becki Falwell and Jerry Falwell took part in some of the liaisons as a voyeur.

Mr Falwell told the Associated Press he resigned only because “I don’t want something my wife did to harm the school I’ve spent my whole life building”. “I never broke a single rule that applies to staff members at Liberty,” he said.

Becki Falwell also spoke with AP, saying she and her husband “have the strongest relationship and Jerry is the most forgiving person I’ve ever met”. “It’s a shame that Christians can’t give us the same forgiveness that Christ gave us.”

Mr Falwell, 58, had already been on leave since earlier this month after alumni recoiled at a photo he posted on social media that showed him with his pants unzipped, stomach exposed and arm high around the waist of his wife’s pregnant assistant. Mr Falwell has said the photo was taken at a costume party during a family holiday.

The latest controversy began to unfold late on Sunday, when The Washington Examiner published a statement from Falwell disclosing his wife had had an extramarital affair. It said the man involved had been threatening to reveal the relationship “to deliberately embarrass my wife, family, and Liberty University unless we agreed to pay him substantial monies”.

On Monday, Reuters published Giancarlo Granda’s account of the relationship, including what the news agency said was an audio recording of a phone call between the Falwells and Granda.

Mr Granda denied any such trying to extort the couple, saying he was seeking to negotiate a buyout from a business arrangement he says he had with them.

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