In a clip posted to YouTube called "Shred the Love: The Director's Cut," a man is shown building the frame and then completely shreds a copy of "Girl With Balloon." A caption in the video notes that "In rehearsals it worked every time."
"It does look like paper coming out, but there is a chance it could be a fine linen," said Danielle Howe, who works at John Jones, a London-based canvas supplier, told The New York Times. "(But) it's difficult to determine without looking at the work in person."
Alex Branczik, Sotheby's head of contemporary art in Europe, repeated that the auction house was not privy to Banksy's stunt, the BBC reported.
"Some people think the auction house were in on it, they weren't," Banksy said in an Instagram post on Thursday that pointed people to the YouTube video.
In an interview with The Art Newspaper, Branczik said Sotheby's had asked Pest Control, Banksy's official authentication body, if the frame could be removed before the auction.
“Pest Control said very clearly: The frame is integral to the artwork,” Branczik told the magazine. "Which it was. Just not in the sort of way that we thought.”
The buyer of the artwork has kept it, the Times reported. It has been renamed "Love Is in the Bin," after Pest Control issued a new authentication certificate, the newspaper reported.