Shakira, Usher, Adam Levine and Blake Shelton have performed together for the first time.The four stars - who all serve as coaches on the new season of  The Voice in the US - performed a rendition of The Beatles’ classic ‘Come Together’.The performance was aired during the season’s opening episode on March 25, with Shakira and Usher taking over as coaches from Christina Aguilera and Cee Lo Green.The rendition of the Brit hit sees Usher and Shelton on guitars, Levine on drums and Shakira playing the harmonica. Agencies