Yesterday Beyonce and Jay Z were together for the Roc Sports Brnch – greeting industry folks like they were hosting a DINNER PARTY at their home (It was kinda SURREAL to be there). But when word got around that RIHANNA was on her way . . . the mood changed.

MediaTakeOut.com can report that Beyonce LEFT the main area, and went to a discreet private area – never saying ONE WORD to Rihanna. We can’t tell you WHY Beyonce is doing this . . . but she is DEFINITELY AVOIDING RIHANNA.

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Of course, all the rumors about Jay and Rihanna F*CKING IN THE PAST – may have something to do with it.

This is not the FIRST TIME that Beyonce excused herself when Rihanna was in her presence. Last month, Beyonce and Jay Z attended the ROC SPORTS boxing match at Madison Square Garden in New York City. Beyonce was set to come out with Jay .. . until she learned that RIHANNA was in the building. Beyonce then STAYED BACK STAGE for the entire event . . . and left with Jay.