"The biggest piece of advice we've been given is, 'Don't talk to her about horses unless you know what you're talking about because she's an expert,'" he told CBS Sunday Morning correspondent Mark Phillips.
The Queen is an avid and successful horse breeder and racer and has been to Kentucky before privately to oversee her stock, but she'd never been to the Big Show of the Derby.
Most of it would have looked familiar to her. She often attends the big social-occasion race meetings at home. Some of it, though, might have seemed strange.
If the Queen placed a bet, it was (like the visit) private.
The whole day and in fact the Kentucky weekend was a respite before she resumes her state visit in Washington tomorrow.