Fashion designer Karl Lagerfeld denies having called French President Francois Hollande an "idiot", suggesting the purported remark reported in a magazine came from a mistranslation.

"Obviously I did not say that. So I don't have to apologise because I didn't say it," the Paris-based German designer told France 2 television.

"Unfortunately I do not speak Spanish, so I don't really know what they said," said the creative director of French fashion-house Chanel.

According to an interview with the Spanish edition of Marie Claire, Lagerfeld called Hollande - who famously said he does not like the rich - an idiot for imposing a 75 per cent tax on incomes exceeding one million euros (NZ$1.6 million) annually.

Lagerfeld said he had a roaming, three-hour conversation with the magazine, covering topics including the press's "horrible" treatment of Bernard Arnault, who heads the LVMH luxury giant, after he applied for Belgian nationality.

The designer refused to criticise Hollande's new fiscal policy but said he regretted the luxury industry was "treated almost like it is plague-ridden", even though it "brings a lot" to France.

Langerfeld later said it was "frankly absurd" that he could have insulted Hollande, saying he found the president "funny, spiritual and very, very intelligent".

On Friday, Hollande's former companion and a one-time presidential contender Segolene Royal led the charge against Lagerfeld, demanding an immediate apology.