Kelly to Regis: You're WHAT?!?

1/18/2011 2:10 PM PST

Regis and Kelly -- Kelly Ripa Blindsided By Regis' Retirement News Before Live! With Regis & Kelly

Sources connected with "Live! with Regis & Kelly" tell TMZ ... Regis Philbin blindsided Kelly Ripa with his retirement announcement today ... telling her less than 15 minutes before they went on the air.

We're told Kelly was "stunned" that Regis didn't tell her well in advance.  But one source connected with the show tells us, "She wasn't upset."

Our sources say Regis felt if he talked about it before making the announcement, it would have leaked out.