It’s still not official but UFC president declared during a UFC 157: Rousey vs. Carmouche question and answer session that:
“GSP (23-2 MMA, 17-2 UFC) is going to defend his title against Nick Diaz (26-8 MMA, 7-5 UFC). Anderson Silva (33-4 MMA, 16-0 UFC) will defend his title this summer, and before the end of this year we will soon see a super fight with either GSP and Anderson Silva, or Anderson Silva and Jon Jones (17-1 MMA, 11-1 UFC). One of them is coming.”
You might like to hear it with your own ears: