Damian Green, Britain's First Secretary of State and effective Deputy Prime Minister, resigned Wednesday after an investigation found he misled police about the presence of pornography on his office computer, according to multiple media reports.
Mr Green's departure from the frontbench has left a major hole at the heart of Mrs May's Government with speculation now growing over who she could appoint as her replacement First Secretary of State.
Mr Green has continued to deny what he called "unfounded and deeply hurtful" claims that he downloaded or viewed the material.
"I think that doesn't mean it isn't a very sad moment", he said.
It is not likely that Mr Green's exit will suddenly unleash another bout of turmoil, writes the BBC's Political Editor Laura Kuenssberg, in her blog, but it does leave her a "lonelier figure".
May said she asked Green for his resignation after the investigation concluded he had not been open about the matter. She said he had fallen short of the standards expected of him.
Green was a vital political ally who acted as a de facto deputy prime minister and supported May in her hard Brexit negotiations.
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"It is therefore with deep regret, and enduring gratitude for the contribution you have made over many years, that I asked you to resign from the government and have accepted your resignation", she said. His removal will cost her an important supporter as she tries to balance competing visions of Brexit within her Cabinet.
The Cabinet Office investigation did not rule on allegations made by writer Kate Maltby that Mr Green sexually harassed her.
The probe was prompted by Ms Maltby's allegations - denied by My Green - but it was later widened to include claims legal pornography had been found on his computer after a police raid on his Commons office in 2008.
Kate Maltby's parents, Colin and Victoria, said in a statement they were not surprised to find that the inquiry found Mr Green to have been "untruthful as a minister, nor that they found our daughter to be a plausible witness".
She wrote in an article for The Times in November that Green touched her knee "fleetingly" in a London pub in 2015, when the two were meeting to discuss the possibility of a future career for her in politics.
Green is among a number of British politicians who have stepped down or been forced out in recent weeks as a wave of allegations of sexual harassment has surfaced.