Ashlee Simpson ( born October 3 , 1984 ) is an American pop rock singer , songwriter , and actress , and younger sister of pop singer Jessica Simpson . Ashlee Nicole Wentz ( nÃ e Simpson ; born October 3 , 1984 ) , is an American recording artist and actress . Simpson , who is the younger sister of pop singer Jessica Simpson , rose to prominence in mid-2004 through the success of her number-one debut album Autobiography and the accompanying reality series The Ashlee Simpson Show .