What does Genesis 35:22 mean?

While Israel was living there, Reuben slept with Bilhah, his father's concubine, and Israel found out. Jacob had twelve sons. Genesis 35:22 - Modern Text Bible

(Reuben, Jacob's oldest, sleeps with Bilhah, which is a serious betrayal. This act will have consequences later. The verse also notes that Jacob has twelve sons, setting up the tribes of Israel.)