What is the name of althualpa's half-brother?

Huáscar

Explanation:

Atahuallpa or Atawallpa (c. 1502 – 1533) was the 13th and last sovereign (the last de jure emperor being Túpac Amaru) emperor of the Tahuantinsuyo, or Inca empire. He became emperor upon defeating his younger half-brother Huáscar in a civil war sparked by the death of their father, Inca Huayna Capac, from an infectious disease thought to be malaria or smallpox. During the civil war, the Spaniard Francisco Pizarro crossed his path, captured Atahuallpa, and used him to control the Inca empire. Eventually, the Spanish executed Atahuallpa, ending the Inca Empire (although several weak puppet successors followed him.)

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