(Noel Vasquez/Getty Images)

There's a big mystery in Tampa. Who is the "TBA" who will address the convention Thursday night just before Marco Rubio and Mitt Romney?

It's a prime slot on the final night of the convention. The convention hall has been buzzing with the possibility - almost the expectation at this point - that it will be Clint Eastwood, who endorsed Romney earlier this year.

You'll recall that some Republicans were frustrated by Eastwood's appearance in that Chrysler Super Bowl ad about "halftime" in America. Romney, of course, opposed the auto bailout that saved Chrysler.

I talked with Diane Sawyer about the Eastwood question on "World News." Take a look after this piece by Jon Karl: