AT: "xx" Toru was the son of Hoshi Sato in an alternate timeline in which the NX-01 Enterprise was sent back 117 years into the past. He had a sister named Yoshiko.
In the normal timeline, Sato learned of Toru by searching the database of the alternate Enterprise, but refused to learn who the father was, believing that "some things are better left a mystery". (ENT: "E²")