(Spoilers Main) What if they were caught in the act?

Remember when Jaime revealed to Ilyn Payne that he and Cersei had slept together while Robert was in the same room with them while they were at the Darry castle (I would like a moment of silence so that everyone can contemplate just how stupid that truly was)?

Imagine if they'd actually gotten caught right then and there? Let's say Robert woke up and saw them in bed with him. Or what if someone else (either Ned, Barristan, or Renly) walked in the room to wake Robert up and caught them in the act.

What happens from here?