וּבְנֵ֨י רְאוּבֵ֥ן בְּכֽוֹר־יִשְׂרָאֵל֮ כִּ֣י ה֣וּא הַבְּכוֹר֒ וּֽבְחַלְּלוֹ֙ יְצוּעֵ֣י אָבִ֔יו נִתְּנָה֙ בְּכֹ֣רָת֔וֹ לִבְנֵ֥י יוֹסֵ֖ף בֶּן־יִשְׂרָאֵ֑ל וְלֹ֥א לְהִתְיַחֵ֖שׂ לַבְּכֹרָֽה׃
E i figli di Ruben, primogenito d'Israele — poiché egli era il primogenito, ma, avendo profanato il giaciglio di suo padre, la sua primogenitura fu data ai figli di Giuseppe, figlio d'Israele, ma non per essere iscritto nella genealogia come primogenito.
Rashi
And the sons of Reuben the firstborn of Israel Now if you ask: since he was the firstborn, why did the kingship not emanate from him? He was indeed the firstborn, but when he desecrated his father’s bed, his birthright was given to the sons of Joseph. Now if you ask, if so, why did the sons of Joseph not reign? He therefore says, “but not to be reckoned in the genealogy as the first born,” [i.e., the sons of Joseph were not meant] to take the share of the kingship, but only the birthright, because Judah was the most fit to reign even if Reuben had not defiled the birthright and it had not been taken from him.