A British teenager says that Banksy gave him a signed print after he helped the street artist pick up paints that had fallen out of his bag, Daily News reports. The incident took place on a train in Oxenholme, England.

Fourteen-year-old Ben Azarya told Daily News that a fellow passenger who introduced himself as Robin Banks gave him the artwork and told him, “This will be worth about £20,000—have a good life, brother.”

Describing the incident the boy said, “He opened his rucksack and had a gas mask and spray paints inside. He got out a piece of paper and had colors marked on it of what he had been trying out, and he dropped his colors.” He continued, “I picked them up for him and after that he started signing it in weird letters and numbers. He said ‘do you know who Robin Banks is?’”

Azarya described the elusive street artist as white and in his late 40s. He looked “really wacky,” and was wearing “scruffy clothes” such as “jeans with paint on,” and a “fluffy hat, which looked really old.”

Azarya and his mother Jan have since contacted Bonhams Auction House, who advised them to have the artwork authenticated. The boy plans to sell the painting to “get a new phone and save the rest.”