O Pantera Negra é um membro da família real do Reino de Wakanda e o título "Sua Alteza" é tipicamente reservado para a realeza. consulte a Wikipédia
The character is usually depicted as the king and protector of Wakanda, a fictional African nation. Chadwick Boseman portrays the Black Panther in Captain America: Civil War (2016) and is set to return in Black Panther (2018), both set in the Marvel Cinematic Universe.
Ou como está escrito no Wiki da Marvel que você vinculou:
T'Challa is heir to the centuries-old ruling dynasty of the African kingdom Wakanda, and ritual leader of its Panther Clan. His mother died in childbirth, earning him the enduring hatred of his adopted elder brother, Hunter, who also resented T'Challa for supplanting him in the royal household.