וַֽיִּלְכְּדָ֛הּ עָתְנִיאֵ֥ל בֶּן־קְנַ֖ז אֲחִ֣י כָלֵ֑ב וַיִּתֶּן־ל֛וֹ אֶת־עַכְסָ֥ה בִתּ֖וֹ לְאִשָּֽׁה׃
And Othniel the son of Kenaz, the brother of Caleb, took it; and he gave him Achsah his daughter to wife. .
Rashi on Joshua
He [Osniel] was the brother of Caleiv. He was his brother from his mother.17After Caleiv’s father, Yefuneh, died, his mother married Kenaz and she gave birth to Osniel.