In 2016, a small, long-lost Rembrandt painting (The Unconscious Patient) was found in a basement in New Jersey. It was initially valued by a local auction house at $800. However, several art collectors recognized its true value, which resulted in a winning bid of $870,000. – WTF Fun Facts
Source: https://www.reuters.com/article/us-new-jersey-rembrandt-idUSKCN0Y226R