R&B superstar Rihanna announced Tuesday that up-and-coming rapper J. Cole has been upgraded to the "official opening act" on her current "Loud" tour, after Cee Lo Green backed out earlier in the week.  J. Cole was already performing on the tour, but Tuesday's announcement means that a replacement won't be found for Green, and J. Cole will be performing right in front of Rihanna.  The singer made the announcement on her Twitter page.  J. Cole, a Jay-Z protege, is set to release his debut album, "Cole World: The Sideline Story" on September 27th.  The "Loud" tour continues in the US through July 24th before heading over to Europe, wrapping up in late December.