《北史·列传·卷五》
元匡上奏说，亲王和始封的藩王、二代藩王的妻子，都有王妃的封号，而三代藩王以下，都称为妻。
匡奏亲王及始籓、二籓王妻，悉有妃号。而三籓以下，皆谓之妻。
Yuan Kuang memorialized that the wives of the Prince and the first-generation feudal lords and the second-generation feudal lords were all given the title of Princess, while the wives of the feudal lords below the third generation were all called wives.