An original watercolor illustration for the cover of the first Harry Potter book has sold for $1.9 million at auction, making it the most expensive piece of Potter artwork ever, reports the BBC. The illustration for Harry Potter and The Philosopher’s Stone shows Harry waiting for his train to take him to Hogwarts. The piece by Thomas Taylor—only 23 when he completed the work in two days—sold at Sotheby’s New York on Wednesday, per CBS News. “This is really the first visualization of Harry Potter and the wizarding world,” said Kalika Sands from Sotheby’s. The artwork had been expected to sell f…