Boris Johnson was aware of a previous formal complaint about Chris Pincher's behaviour from over two years ago, it has been claimed.
A disciplinary process overseen by the Cabinet Office at the time then confirmed the disgraced MP's misconduct in a report.
It is understood the PM and then-Foreign Secretary Dominic Raab knew of issue when it arose, according to the BBC.
Mr Pincher was a Foreign Office minister when the complaint was made between 2019 and 2020.
It raises fresh concerns as to whether Mr Johnson knew before appointing the 53-year-old as deputy chief whip in February during a Cabinet reshuffle - a role he quit last Thursday following fresh allegations.
The Member of Parliament for Tamworth was suspended from the Conservative Party last week after being accused of groping two men at a London private members' club.
However, he has since said he will not be resigning his seat and is seeking medical help.
He has also denied multiple allegations of inappropriate behaviour dating back years.
Mr Pincher was appointed FCDO minister in July 2019 by the PM and remained in that position until the following February.
Mr Johnson and Mr Raab were aware of the formal complaint during that period, reports the BBC.
Mr Johnson's spokesman told the broadcaster the PM was aware of media reports and some allegations that were "either resolved or did not progress to a formal complaint".
A government spokesperson told the Mirror: "There are robust procedures in place for any members of staff to raise allegations of misconduct.
"It is long-standing policy not to comment on any matters involving individual cases."
