Banksy has revealed how he installed a shredding machine inside his iconic artwork Girl With Balloon so it would self-destruct if sold at auction.

The artwork was ripped to shreds moments after it went under the hammer for more than a million at Sotheby's auction in London.

Banksy made the revelation that he created the shredder in a video he posted on Instagram.

In it, he is seen building the shredder, which he said is operated by a remote device.

Footage showing the shocking moment the shredder whirred into life at Sotherby's is also included in the video.

He explains: 'A few years ago I secretly built a shredder into a painting in case it was ever put up for auction...'

However he may have inadvertently helped to reveal his own identity because other people filming the scene caught him on camera.

The man who is believed to be the person who shot the video that Banksy uploaded bears a strong resemblance to Robin Gunningham who has previously been named as the elusive artist.

The artist also dropped a strong hint that he was behind the shredding of his iconic artwork in an interview with Channel 4.

In the interview, the Bristol artist is said to have quoted Mikhail Bakunin, telling flagship news presenter Krishnan Guru-Murthy: 'The urge to destroy is also a creative urge.'

However, far from devaluing the art, experts believe that last night's stunt may have actually doubled the price of the work because of the huge interest it generated.

Immediately after the auction Alex Branczik, Sotheby's senior director and head of contemporary art in Europe said: 'It appears we just got Banksy-ed.

But today Joey Syer, co-founder of MyArtBroker, said: 'The auction result will only propel this further and given the media attention this stunt has received, the lucky buyer would see a great return on the £1.04million they paid last night.

'This is now part of art history in its shredded state and we'd estimate Banksy has added at a minimum 50% increase to it's value, possibly as high as being worth £2million plus.'   

As the sale concluded to a phone buyer the canvas suddenly passed through a remotely activated shredder installed in the frame and an alarm went off.

Posting a picture of the moment on Instagram, Banksy wrote: 'Going, going, gone...' 

The artwork was photographed dangling in pieces from the bottom of the frame as auctioneers removed it from the wall.

The Girl With Balloon, which was signed and acquired from Banksy by a mystery buyer in 2006, was the final piece auctioned in a contemporary art sale on Friday night.

The framed stencil painting is one of Banksy's most recognised murals, and the original appeared on a shop wall in east London, depicting a girl reaching towards a heart-shaped balloon.   

It is not known who the successful bidder is but Sotheby's said they are talking to them and that they were 'surprised' by the bizarre stunt.

Alex Branczik, Sotheby's senior director and head of contemporary art in Europe said: 'It appears we just got Banksy-ed.

'We have talked with the successful purchaser who was surprised by the story.

'We are in discussion about next steps.'

Sotheby's described the work ahead of the sale as 'authenticated by Pest Control', the handling services organisation that acts on Banksy's behalf. It was signed and dedicated on the reverse and had been acquired by the vendor directly from the artist in 2006, the auction house said.   

Girl With Balloon is one of graffiti artist Banksy's most famous murals.

The imagery was first spotted on the wall of a shop in 2002, in Great Eastern Street, east London.

It features just two simple shapes, with the statement: 'There is always hope'. 

The girl depicts a Syrian refugee, an imagery which Banksy uses many times in his murals.

The iconic mural was last year voted the nation's favourite artwork.

The image was chosen above the likes of Constable's Hay Wain and Jack Vettriano's Singing Butler.

Featuring on the shop wall for more than 12 years. it was also set to be  removed and sold in 2014.

Events company Sincura Group, which controversially removed another Banksy mural in Tottenham, said would exhibited the work before selling it for about £500,000.

A man who works in the printing shop said in he had not seen the Banksy mural for years because it was been covered with boards.

In March 2015, the third anniversary of the Syria conflict, Banksy reworked the painting to depict a Syrian refugee and added #WithSyria.

The image was later projected on the Eiffel Tower and Nelson's column in Paris.

Justin Bieber famously got the image tattooed on his arm, which was blasted by Banksy himself.

A Facebook page which is thought to represent the mysterious Banksy posted a photo of the ink with the caption: 'controversial.'

A version of the artwork painted onto the cardboard backing of an Ikea frame sold for £73,250 in 2012.

However, there is speculation that the shredded art could be fake. It is not known who bought the work from Banksy in 2006 and whether or not they were in on the stunt.

One person on Twitter said: 'It's not shredded. It's still rolled up inside the frame. A pre-torn canvas rolled out from behind the one in front that is rolled up behind itself.'

It would appear that Sotheby's did not know about the stunt, though, nor the buyer who now simply owns shreds of paper. Whether or not he or she will still have to pay the huge price is also unclear.

But some people on social media claim that Sotheby's was actually involved in the prank.

One said: 'How did all of the experts at Sotheby's who evaluated the piece fail to notice the piece contained a shredding mechanism?'

People online also thought that Banksy's prank was a rebellious statement against the art world because his pieces are made to be 'experienced' and not owned.

One person on Twitter said: 'Banksy was clearly making a statement about anyone who thinks you can actually own his art. He's essentially saying art is free and isn't meant to be owned'

Celebrities were quick to pay tribute to the unusual prank on Twitter.

Broadcaster Jeremy vine posted on Twitter: 'This is incredible.'

Star of Dragons Den Deborah Meaden said: 'Banksy is officially the coolest, most poignant person on Earth. Of course it's a publicity stunt but it's publicising the sheer insanity of where we place our values.'

Present Richard Bacon said: 'It must be a lot of fun being Banksy. Making a (theatrical) point about art that no one else in art can make.'

Art critic Jerry Saltz said: 'I never much liked Banksy's art and act. This I love. I am yours Banksy.' 

Banksy is known for rebelling against the art world.

In 2007 Sotheby's sold three of Banksy's works. The day after the sale he updated his website with an image of an auction house and the people bidding on a picture with the written words 'I Can't Believe You Morons Actually Buy This S**t'.

He came to prominence through a series of graffiti pieces that appeared on buildings across the country, marked by deeply satirical undertones.

The self-destruction was the latest in a long history of anti-establishment statements by the street artist.

Other recent works included the opening of Dismaland, his dystopian, Disneyland-esque theme park in 2015, which he described as a 'family theme park unsuitable for children'. 

Since Banksy made his name with his trademark stencil-style 'guerrilla' art in public spaces - on walls in London, Brighton, Bristol and even on the West Bank barrier separating Israelis and Palestinians - his works have sold for hundreds of thousands of pounds.

He has dozens of celebrity collectors including Brad Pitt, Angelina Jolie and Christina Aguilera.

He is also known for his headline-making stunts, such as leaving an inflatable doll dressed as a Guantanamo prisoner in Disneyland, California, and hanging a version of the Mona Lisa - but with a smiley face - in the Louvre, Paris.

But perhaps his most provocative statement, and the one that generates the most publicity, is the fact that Banksy's true identity has always been a jealously guarded secret, known to only a handful of trusted friends.

A network of myths has grown up around him including that his real name is Robin Banks or the he used to be a butcher.

There is also the rumour that his parents don't know what he does, believing him to be an unusually successful painter and decorator.

Then there's the suggestion that Banksy is actually a collective of artists and doesn't exist at all.

Such is the curiosity about Banksy that when he threw a pizza box into a bin in Los Angeles, the box resurfaced on auction site eBay, with the seller suggesting that the few anchovies left inside might yield traces of his DNA.