Are Britney Spears and Rihanna collaborating for the first time?  It sound like it.  The two pop stars went to Twitter to Sunday evening to announce Spears would be appearing on a new remix of Rihanna's surprise hit single "S&M."

Rihanna started it off with "I got a #SEXY collabo comin your way supa dupa soon!!!! OH YEAH!!! By popular demand…."  She then followed up with, "Its BRITNEY BITCH!!!!"

Spears then tweeted, "@rihanna You're such a tease! I like it, like it…."

Rihanna responded with, "MAJAH Rihmix to S&M MAJAH!!!!"

Spears replied with, "You think they're ready Ri Ri?"

Rihanna came back with, "One of the biggest worldwide popstars! U gangsta #EPIC"

"You ain't so bad yourself honey," Spears says ending the Sunday night conversation.

What's unclear is why the stars are collaborating on an "S&M" remix now.  "S&M" is currently number two on Billboard's top 100 chart.  Spears' "Femme Fatale" album debut in the top slot last week and her new video for "Til the World Ends" has pushed the song back up to the top five on iTunes.  How this would help either singer, besides a historical footnote, remains to be seen.

Look for more on this story as more info becomes available on HitFix.