Correlation not causation- Question

A good lie requires a backstory. In order to thoroughly convince someone of the legitimacy of a lie, one must point out side details that back their argument, out or pure coincidence. There is no clear historical evidence that Elizabeth I ever had an affair with Robert Dudley, however The Virgin's Lover suggests other wise. Philippa Gregory can be blatant about it at times, and other times refrains to small hints that could be dismissed as coincidence.

What details does Phillipa Gregory use, to convince us that Elizabeth and Robert are having an affair, without being blatantly obvious about it?