Gwen Stefani will be back in familiar quarters when she returns to her post as a coach for season 19 of “The Voice.” The pop superstar, 50, is reuniting with her longtime beau Blake Shelton, 43, Kelly Clarkson and John Legend in what felt like a swift hiatus after she stepped away from the reality competition series as a full-time coach following season 17. At the time, she was replaced by frequent vocal mentor Nick Jonas.