Complex sentence: Ultimately, Jay-Z was selected as the featuring artist; "Upgrade U" becoming his second collaboration with Knowles on "B'Day"--the first being "Déjà Vu" (2006).
Split into simpler sentences: Ultimately, Jay-Z was selected as the featuring artist. Hence, "Upgrade U" became his second collaboration with Knowles on "B'Day", the first being "Déjà Vu" (2006).