U.S. pop stars Katy Perry and John Mayer have broken up again, UsMagazine.com said Wednesday. The website cited unnamed sources as saying Perry's travels to Europe and plans for a lengthy concert tour contributed to the end of their romance. Perry, 29, and Mayer, 36, first debuted as a couple in 2012. They split up that fall, then again last March and ultimately reunited. They released the duet "Who You Love" in December.