Alun Cairns has written to Boris Johnson to tender his resignation as Secretary of State for Wales.
It's after he was accused of “brazenly lying” about his knowledge of an allegation that a fellow Conservative candidate had sabotaged a rape trial.
Rival parties have welcomed the move but now say the Cabinet minister should step down as candidate in the December 12 General Election.
In his resignation letter, Mr Cairns wrote: "This is a very sensitive, and in light of continued speculation, I write to tender my resignation as Secretary of State for Wales.
"I will cooperate in full with the investigation under the Ministerial Code which will now take place and I am confident I will be cleared of any breach or wrong doing."
It came just as the Prime Minister was about to launch the Conservative election campaign on the steps of Downing Street.
Welsh Conservative Party chairman Lord Davies of Gower thanked Mr Cairns for his work in the role and wished him well for the future.
However, Christina Rees, shadow secretary of state for Wales said his resignation was “a shoddy halfway house that will fool nobody”.
She urged him to apologise and stand down as a candidate, saying: “He has still not explained his behaviour … worse still, neither he nor any senior Welsh Tory have apologised to one person who most deserves it - the victim herself”.
Meanwhile Plaid Cymru's Liz Saville Roberts said the incident "proved unquestionably" that Mr Cairns is "not fit to hold ministerial office".
She added: "I hope that Alun Cairns' resignation as secretary of state proves to be some solace to the woman at the centre of this case, who still has received no apology from the Conservative Party."
Mr Cairns is the first cabinet minister to resign during a general election campaign in the last centrury
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