He was the son of Gonji, the younger brother of the 22nd king Munju who returned to Baekje from Yamato Japan in 477 after hearing of the fall of the Baekje capital. Gonji died in that year, and like Munju may have been murdered by Hae Gu. Dongseong appears to have been promoted to the throne by the Jin clan that prevailed over Hae Gu's rebellion. After Samgeun died without children, the throne passed to Dongseong