Keliʻiahonui was born May 13, 1869 at Kaʻalaʻa at the mouth of the Pauoa Valley, in Honolulu, on the old homestead of his aunt Queen Kapiʻolani. He was baptized by Bishop Thomas Nettleship Staley of the St. Andrew's Cathedral. His genealogy centered mainly on his ancestry as an heir of his great-grandfather Kaumualiʻi, the last ruling King of Kauaʻi. He shared his name with his great-uncle Kealiʻiahonui who was sometimes called the last prince of Kauaʻi. His mother Princess Victoria Kinoiki Kekaulike was sister of Queen Kapiʻolani. His father was High Chief David Kahalepouli Piʻikoi, first cousin of King Kalākaua. Keliʻiahonui was initially educated at St. Alban's College (now ʻIolani School) and Punahou School. In 1885, he and his brothers David Kawānanakoa and Jonah Kūhiō Kalanianaʻole were sent abroad along with to attend Saint Matthew's School, a private Episcopal military school in San Mateo, California.

In 1874 the Kalākaua Dynasty ascended to the throne of the Kingdom of Hawaiʻi, ending the Kamehameha Dynasty. By royal proclamation, Keliʻiahonui and his brothers were created Princes with the style His Highness in 1883 in honor of Kalākaua's coronation ceremony. He was fifth-in-line of succession to the Hawaiian throne after Liliʻuokalani, Likelike, Kaʻiulani, and his brother David Kawānanakoa. He was elevated to fourth-in-line to the throne after Princess Likelike's death seven months before his own. The three brothers were known as the Piʻikoi Brothers or the "Three Princes". Being the middle son he was in a difficult position. A year younger than his brother David, he was physically smaller than either of his brothers. He also fought illness more frequently. His brothers were adopted sons of the king and queen. He was adopted in the Hawaiian tradition of hānai to his aunt Princess Poʻomaikelani, while his brothers were adopted by King Kalākaua and Queen Kapiʻolani.

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