The French foreign minister has accused Boris Johnson, now his counterpart in the UK, of lying "a lot" while he was a leader for the Leave campaign.
"I don't have any doubt about Boris Johnson," Jean-Marc Ayrault said during an interview with French radio Europe 1.
"You know his style and his methods. He lied a lot during the [referendum] campaign."
The two men have met in the past when both were mayors - Mr Ayrault as mayor on Nantes and Mr Johnson as mayor of London.
Alex Salmond has dismissed Boris Johnson as a "court jester" but said the real "test" will be whether Theresa May allows cabinet members with more gravitas to shape her policies.
"The real issue is this - are the serious politicians ... going to be playing second fiddle to someone like Boris Johnson," the former SNP leader told ITV News.
"Has she [Prime Minister May] just got Boris Johnson to give everyone a laugh, or is she going to let him, I don't know, give away the Channel Islands by mistake in negotiations."
Mr Salmond, who is the SNP's spokesperson on foreign affairs, said that with Mr Johnson as foreign minister "everyone is going to have a giggle at our expense", but added that given recent political manouvering "perhaps that's not a bad thing".
This is the moment that a US state department official struggled to regain his composure after learning that Boris Johnson had been appointed as the new British foreign secretary.
Mark Toner, deputy spokesman for the equivalent to the UK foreign office, appeared to struggle not to laugh as he was told the news during a briefing with journalists.
After getting his facial gymnastics under control, he said that the US would "always be able to work with the British" as the relationship "goes beyond personalities".
Hardly a ringing endorsement for Mr Johnson.
John Kerry has confirmed he spoke to newly appointed Foreign Secretary Boris Johnson this morning and said the US-UK special relationship is "as essential as ever".
The US Secretary of State also stressed US support for a "sensible and measured approach" to Brexit.
Boris Johnson has already made a phonecall to the US in his role as foreign secretary.
Johnson rang Secretary of State John Kerry to tell the US that the country was "at the front of queue" after Brexit.
Johnson has also been pictured addressing 500 staff at the Foreign Office to set out his vision for the future of the department.
Boris Johnson has told ITV News he is excited to play a part in the UK's "new relationship with Europe and the world", after he was named foreign secretary in prime minister Theresa May's new cabinet.
When asked if he agreed he had a number of people to apologise to, including President Obama, the new foreign secretary of the UK said: "The United States of America will be at the front of the queue."
Johnson was accused of racism after he suggested during the Brexit campaign that Barack Obama may have an "ancestral dislike of the British empire" because of his heritage.
The US State Department has said it is looking forward to working with newly-appointed foreign secretary Boris Johnson.
The US will always be able to work with British officials because of its "deep, abiding" relationship with Britain, State Department spokesman Mark Toner said at a press conference.
David Cameron has led the Conservative party "magnificently", Boris Johnson said.
The former London Mayor said: "I think it has been a fantastically distinguished period of government. I think he's led our party magnificently."
He added: "He will be remembered as a great reforming prime minister."