Rashi on Numbers 32:12/רש"י על במדבר ל״ב:י״ב

1הקנזי [CALEB THE SON OF JEPHUNNEH] THE KENEZITE — He (Caleb) was the stepson of Kenaz (and therefore he is termed here the Kenezite), and Caleb's mother bore Othniel to him (to Kenaz) (and for this reason Othniel, the son of Kenaz is described in Joshua 15:17 as Caleb’s brother) (Sotah 11b).