Boris Johnson told his new director of communications Guto Harri, "I will survive", by singing him lines from the Gloria Gaynor song as he appointed him to the post.
Mr Harri was hired after a string of resignations from No 10 amid turmoil over parties held during lockdowns.
The aide told a Welsh news website he saw the PM on Friday afternoon.
He also said his new boss was "not a complete clown, he's a very likeable character".
Mr Harri told Golwg 360 that after exchanging lines from the 1970s disco hit, and "a lot of laughing", he and Mr Johnson "sat down to have a serious discussion about how to get the government back on track and how we move forward".
He added: "90% of our discussion was very serious but he's a character and there is fun to be had. He's not the devil like some have mischaracterised him."
Mr Johnson has been under increasing pressure from his party - including calls to resign from MPs - after revelations that numerous rule-breaking gatherings were held in Downing Street during Covid lockdowns.
An initial report into the parties by senior civil servant Sue Gray said there had been "a failure of leadership", leading to the PM promising a shake-up of staff.
Five aides resigned from No 10 last week - three of whom had been linked to the lockdown events in Downing Street.
But Munira Mirza, one of the PM's longest standing allies, quit in objection to the PM's false claim that Labour leader Sir Keir Starmer failed to prosecute Jimmy Savile.
Mr Harri was one of the first new appointments to fill the roles, along with Cabinet Office Minister Steve Barclay, who has taken the chief of staff role.
Asked about the shake-up at No 10, Mr Johnson told reporters on Monday: "Everybody at No 10 and the Treasury are working together in harmony to deal with the big problems the country faces."
But Sir Keir reiterated his calls for the PM to resign, saying: "Nothing will really change until the person at the top changes as all routes lead to the prime minister and that's the change we need to see now."
When asked about the uncertainty over Mr Johnson's leadership, former foreign secretary Jeremy Hunt said the recent turmoil had "affected trust people feel in the entire political process".
"I've received 700 letters as a constituency MP," Mr Hunt told the BBC.
He said many Tory MPs were waiting for the Met Police to conclude its investigation into lockdown parties in Downing Street before making a "final judgement" on Mr Johnson's position.
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