Xubu -

"The Xubu was a tribe of the Xiongnu tribe that flourished between 3rd century BCE to 4th century CE. Chinese annals noted that the Xubu tribe replaced the Huyan tribe, which was an earlier maternal dynastic tribe of the dynastic union with the paternal dynastic tribe Luandi. The traditional system of conjugal unions is a form of the nomadic exogamic society. The male members of the maternal dynastic line were not eligible for the Chanyu throne, only the male members of the Luandi line, whose father was a Luanti Chanyu, and mother was a Xubu Khatun (Queen) were eligible for the supreme throne. A Xubu could only become a Chanyu after a palace coup. - Wikipedia"