Olympic swimming: Leon Marchand and Katie Ledecky create ...

The 15,000-capacity indoor arena has already been dubbed the loudest and best swimming venue in recent memory. Tickets to see Marchand, from Toulouse, have been the hottest property in town.

This, though, was something else - each of Marchand's strokes in the breaststroke leg met with huge roars of "Allez" by a crowd who had turned up with flags, horns and masks of their hero.

His first victory, in a time of one minute 51.71 seconds, was gripping. He trailed by almost a body length at the final turn but overhauled Milak, regarded as the greatest butterfly racer in history, in the final strokes with the crowd on its feet.

Marchand had his first medal ceremony before his next final but, rather than joining Milak and bronze medallist Ilya Kharun of Canada on a lap of honour, he disappeared quickly to recover.

He then completed a pure procession, winning in 2:05.85 to beat Australia's defending champion Zac Stubblety-Cook by almost a second, and the praise soon poured in on social media.

French president Emmanuel Macron labelled him the "merchant of dreams" and a "legend", while World Cup-winning footballer Antoine Griezmann called Marchand the "Little Prince of the Pool".

Marchand has been the rising star of swimming since sending US great Phelps' former coach Bob Bowman a letter, asking to be taken under his wing – a request duly accepted by the much-revered American.

Last year Marchand, known in Japan as 'the new monster', broke Phelps' last remaining world record in the 400m medley which confirmed his status as an elite all-rounder.

He won the 400m medley title here on Sunday too, but in these wins on Wednesday, for which the schedule was altered to allow him the chance of further glory, he beat specialists of their stroke.

"A double Olympic champion in one session - not even Michael Phelps tried that," said BBC commentator and former Olympic swimmer Andy Jameson.

"The audacity. I cannot believe he even tried it, never mind won them both."

The night ended with a final rendition of the French national anthem but it felt like the party would go on long into the night.

Marchand will have a day off on Thursday before returning for his fourth event on Friday - the 200m medley, where he will compete against Britain's Tom Dean and Duncan Scott.