They’re relatively recent, as these things go, but they were made for Qianlong, the longest-reigning emperor (and one of the most popular, still) in Chinese history. They were looted in the Boxer uprising Sino-French war of 1860 and China wants them back, but doesn’t have a legal claim.
update: interesting comments from a specialist on the subject of Qing art and law of possession.
3/3: Sale blocked by spurious bidder citing “patriotic duty.”