When the 23rd century Hikaru traveled back in time from 2286 to 1986, he happened to meet his ancestor Akira on the streets of San Francisco. The child believed Hikaru Sulu to be his uncle, who strongly resembled Akira's eventual descendant.
The 23rd century Hikaru recognized the child almost immediately, having seen pictures of Akira Sulu at various stages in his life. After the meeting was finished, Doctor Leonard McCoy asked Sulu who this child was, and Sulu informed him that Akira was his distant ancestor. (TOS novelization: Star Trek IV: The Voyage Home)