Guto Hari revealed the Prime Minister burst into song after he asked him if he could survive the partygate scandal that has seen a string of high profile resignations.
Speaking to Welsh language news site Golwg360, Mr Hari added the Prime Minister had joked about the time he took the knee on GB news.
He said: “Even though I hadn’t seen him in the flesh for years, we picked up where we’d left off in terms of the tone of our friendship.
“I walked in, saluted and said, ‘Prime Minister, Guto Harri reporting for duty’ and he stood up behind his desk and started to salute too but then he said, ‘What am I doing, I should take the knee for you. ‘
“And both of us were laughing. Then I asked ‘Are you going to survive Boris?’ and he said in his deep voice, slowly and deliberately, and started to sing a little as he finished the sentence, saying ‘I Will Survive’.
“Inevitably, I had to reply with ‘You’ve got all your life to live’ to which he replied ‘I’ve got all my love to give’, so we had a little blast of Gloria Gaynor!
“Nobody expects that, but that’s how it went.”
The new director of communications worked with Mr Johnson when he was Mayor of London, and insisted the Prime Minister was “not a complete clown”.
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He continued: “About 90 per cent of our discussion was very serious but it shows he’s a character and there’s fun to be had with him.
“He’s not a devilish man like some are trying to misrepresent him.”
Mr Johnson lost five of his Downing Street aides in the space of 24 hours on Thursday and Friday, as more MPs sent letters in calling for a vote of no confidence in their leader.
The most painful departure was that of Munira Mirza, who had worked for Mr Johnson for more than a decade.
The policy chief quit on Thursday with a damning letter criticizing Mr Johnson for his use of a “scurrilous” smear against Labor leader Sir Keir Starmer, over the failure to prosecute Jimmy Savile.
Resignations followed from director of communications Jack Doyle, chief of staff Dan Rosenfield, principal private secretary Martin Reynolds, and special adviser in the policy unit Elena Narozanski.
Mr Hari’s appointment comes despite having accused the Prime Minister in 2018 of “digging his political grave” after he compared Theresa May’s Brexit deal to a “suicide vest”.
Earlier on Monday the Health Secretary defended Carrie Johnson, the Prime Minister’s wife over her perceived influence in No 10.
Mrs Johnson issued a rare public statement on Sunday insisting she “plays no role in Government” and has been targeted by “enemies” of the Prime Minister in a “brutal briefing campaign”.
Sajid Javid said: ”I just think as a general rule, a politician’s partner – any politician, any party – should be off limits.
“It’s the politician that has chosen to have a public life… I think the, this whole focus on Carrie Johnson in some of these reports, I think it’s very undignified and very unfair.”
George Holan is chief editor at Plainsmen Post and has articles published in many notable publications in the last decade.