Complex sentence: Sold at auction in 1998 as an early 19th-century German work, it has since been attributed to Leonardo da Vinci by some experts, including Martin Kemp, who, in 2010, made it the subject of his book La Bella Principessa.
Split into simpler sentences: Sold at auction in 1998 as an early 19th-century German work, some experts have since been attributed it to Leonardo da Vinci. One of those experts, Martin Kemp, who, in 2010, made it the subject of his book La Bella Principessa.