But the prime minister’s spokesman denied Downing Street “lied’ when it claimed, last week, that he was unaware of any “specific allegations” against the minister.
Mr Johnson did not originally “recall” being told about the complaint, he said, adding it was “a brief conversation that took place around three years ago”.
The spokesman also conceded the prime minister was told of a separate allegation – when Mr Pincher was promoted in February – but argued that was “unsubstantiated”.
The latest twist to No 10’s version of events comes after the devastating intervention by a former head of the Foreign Office – who revealed Mr Johnson was briefed about the complaint in 2019.
In a letter, Simon McDonald wrote: “Mr Pincher deceived me and others in 2019. He cannot be allowed to use the confidentiality of the process three years ago to pursue his predatory behaviour in other contexts.”
But the prime minister’s spokesman continued to insist the information about Mr Pincher’s behaviour was no reason to bar him from the job as deputy chief whip, with responsibility for Tory MP’s welfare.
He rejected an allegation that he sacrificed a duty of care to MPs and others in order to get his “fixer” into the role, as he fought off attempts to bring him down over the Partygate scandal.
David Lammy, Labour’s shadow foreign secretary, leapt on Mr Johnson’s claim that he was unable to remember being told about Mr Pincher’s behaviour.
“Let that sink in. The prime minister’s defence for promoting Pincher despite the complaint is seriously that he forgot,” he tweeted.
But Mr Johnson’s spokesman insisted No 10 had not misled the public, arguing it “takes some time to establish he was briefed” about the complaint.
“This dates back a number of years. On Friday, it was our belief that he was not informed about that specific incident,” he said.
And he continued to defend the appointment, saying: “It was not raised as a disciplinary issue or anything related to the ministerial code and the prime minister was informed but not asked to take any action.”
The spokesman also denied it is misleading to still claim the complaint was “resolved – when it is now known it was upheld – arguing that is the “terminology that was used”.
The latest scandal to rock No 10 has reignited the determination of Tory rebels to remove Mr Johnson, but there can be no new no-confidence vote for a year unless party rules are changed.
The rebels will aim to seize control of the executive of the 1922 Committee in next week’s elections, in order to try to do that.