The Voice is adding a fourth coach. The NBC music competition has added Grammy Award-winner Queen Latifah as a coach for Season 30. She joins the likes of veterans Kelly Clarkson and Adam Levine and newbie Riley Green. It marks her debut on the show but she has previously been a guest judge on other competition shows such as America’s Got Talent. Latifah is known for songs such as Ladies First and U.N.I.T.Y but she has also had a reputable film and TV career on series such as Fox’s Living Single , daytime talk show The Queen Latifah Show, in movies such as Bessie and as the star of CBS action drama The Equalizer. Season 29, which just ended, saw Clarkson, Levine and John Legend as the three coaches. Season 30, which launches in the fall, will also feature special appearances from former coaches and mentors. Watch on Deadline The Voice  is produced by MGM Television, Warner Horizon Unscripted Television and ITV America.…