The British tourist who carved his girlfriend’s name into the Colosseum says he didn’t realise how old it was.

The bloke went viral after footage of him seemingly etching what appears to be 'Ivan + Hayley 23' into one of the bricks of Rome’s Colosseum - a protected Unesco World Heritage Site - made its rounds across social media.

First posted by YouTuber and American tourist Ryan Lutz earlier this month, the video shows the man defacing the nearly 2,000-year-old building as a blonde woman stands beside him.

After realising he's been spotted, the carver swings around and looks at the camera, before laughing at Lutz who comments: "Are you serious man? That's f**ked up. Stupid a**hole."

See if you can spot the carving... YouTube/@rytz5873

The man was later identified as British man Ivan Dimitrov, a 27-year-old fitness instructor living in Bristol – who now faces a fine and even a potential prison term.

Dimitrov has since written a letter of apology to Roberto Gualtieri, the Mayor of Rome, saying that only now does he realise ‘the seriousness of the deed committed'.

In the letter, published by Il Messaggero today, he said: “Through these lines I would like to address my heartfelt and honest apologies to the Italians and to the whole world for the damage caused to an asset which, in fact, is the heritage of all humanity.”

Dimitrov praised those who ‘guard the inestimable historical and artistic value of the Colosseum with dedication, care and sacrifice’.

He added: “It is with deep embarrassment that only after what regrettably happened did I learn of the antiquity of the monument.”

YouTube/@rytz5873

Dimitrov is now under investigation for damaging a cultural heritage and faces a fine of between €2,500 and €15,000 as well as a prison sentence of two to five years.

His lawyer Alexandro Maria Tirelli told Il Messaggero: “The boy is the prototype of the foreigner who frivolously believes that anything is allowed in Italy, even the type of act which in their own countries would be severely punished.”

Since the footage went viral, it has caused widespread outrage online, with furious commentators saying they hoped the culprit would be found and arrested for the wrongdoing.

Italian Culture Minister Gennaro Sangiuliano said: "This act was offensive to everyone around the world who appreciates the value of archaeology, monuments and history."

Police previously said Dimitrov's girlfriend was not being investigated.

"It is just the man who is accused of scratching his name into the Colosseum, she is not part of the investigation," a Carabinieri officer told The Telegraph.

"We will find them through the normal channels of international police cooperation and there will be a trial."