Selena Gomez and her fiancé Benny Blanco celebrated the last night of Passover with a rockin' Seder. The couple sang their hit Bluest Flame karaoke style during the party. Homemade loaves of challah were shaped to read '4/20' which was the date of the celebration, but could have been a sly nod to the unofficial holiday for those who imbibe in cannabis. Debra Messing and comedian Judy Gold were also in attendance.