Boris Johnson told MPs that he met Russian oligarch Alexander Lebedev, an ex-KGB officer, without official permission.
He said, "I have definitely met him without officials." "I have only met him on very few occasions."
When asked if he had met the Russian billionaire and ex-owner of Evening Standard while he was foreign secretary to Italy in 2018, he replied that he had.
Evgeny Lebedev, the son of Mr Lebedev, was made a member of The House of Lords by Johnson.
There has been controversy surrounding this appointment since The Sunday Times claimed that the peerage was granted despite warnings from security services that it could pose a threat to national security.
The Soviet KGB was the principal Cold War foe of Western security services. President Vladimir Putin was also a KGB officer. Many of Putin's closest aides were KGB friends.
Answering a question from Dame Diana Johnson, Labour's Secretary of State for the Commons Liaison Committee, Mr Johnson was saying yes to a question.
The prime minister stated that he had met the man in question. He was the owner of the London Evening Standard during my time as mayor of London.
"On the occasion that you are referring to, if it was when I was foreign minister, then yes."
Lord Lebedev (current owner of Evening Standard) has denied that the UK is at "security risk."
The Sunday Times reported that the security services' assessment had been withdrawn by Mr Johnson, a long-time friend and confidant of Lord Lebedev.