With the official Prince tribute concert now just a month away, the lineup for the event has finally been announced. Chaka Khan and Stevie Wonder are among the headliners, which also include John Mayer, Christina Aguilera, and recent Grammy nominee Tori Kelly. Wonder and Khan are obviously great choices for this tribute (and not just because the latter’s already performed at one). They were longtime friends of Prince, and collaborated with the Purple One on multiple occasions. Khan had a great hit in 1984 with her cover of Prince’s “I Feel For You” (which Wonder played harmonica on), and they later teamed up for Khan’s Come 2 My House album. And Prince played guitar on Wonder’s “So What’s The Fuss” single in 2005, but their friendship stretches back further than that.