When a subject of an emperor married a Koshu (any husband to a Koshu had to come from a different family, thus a non-sovereign family, as in China and Korea marriage within the family, thus with the same surname, has long been a taboo), it was called尚公主, and the husband was given a title of駙馬都尉 (during the Qing Dynasty, it was 額駙).
臣下が公主を娶る（中国や朝鮮では原則的に同姓不婚であるため、当然ながら公主の結婚相手は臣下に限られる）ことを「尚公主」といい、その夫は駙馬都尉（清朝には額駙）と称呼した。