‘I’m in shock’: Swiss ‘super fan’ whose topless Euro euphoria was shared by London mayor Sadiq Khan touches down in St. Petersburg

Self-declared 'super fan' and reluctant social media sensation Luca Loutenbach has touched down in the Russian city of St. Petersburg for what he hopes will be another emotional night when his beloved Switzerland face Spain.

Devoted Luca Loutenbach became an instant viral hit when he was caught on camera experiencing many of the wild emotions football has to offer as Switzerland beat France on Monday, beating the pre-tournament favorites in the most dramatic of circumstances.

Standing behind a Swiss flag in Bucharest, Loutenbach's ordeal was familiar to millions around the world as he watched Switzerland score two late goals – including a 90th-minute equalizer – before an excruciatingly nerve-wracking penalty shoot-out ended in glory after France superstar Kylian Mbappe was the only man to miss.

London mayor Sadiq Khan shared the shots of Loutenbach with his vast Twitter audience of more than 1.1 million, and the football fanatic, who ripped his top off at one stage during the action, has also been stunned to find himself in national newspapers this week.

"It's crazy what happens," he told a following that quickly built to almost 10,000 on his new Instagram account.

"I'm still in shock. Thank you for all the support during these two days. While I had promised myself never to go on social networks, here I am against my will."

There appear to have been some benefits to Loutenbach's new-found fame as the world's best-known Switzerland fan: he posed surrounded by seats and cabin crew as he set off for the quarter-final clash with Spain on Friday, and filmed himself taking interviews, including from RT Sport, after touching down and brandishing the famous red-and-white flag of the nation he cherishes.

As with many famous faces, though, he has had to deal with a swarm of fake accounts being set up, forcing him to add tags to his pictures so that they are not stolen while appealing to fans to help him report the culprits.

Switzerland are heavy underdogs against three-time Euro champions Spain, facing one of the best teams in the world without their suspended inspirational midfielder Granit Xhaka.

Expressive Loutenbach's reactions will undoubtedly be broadcast to the world as his side seek an unlikely place in the final four – and his legion of admirers will be hoping that his adventure continues against the odds.