During the visit they accept a customary ride in the horse drawn cart around the grounds of Sandringham Castle.
During the trip one of the horses farts and the sound and smell carries all the way through the cart to the royals. Embarrassed by this, the queen whispers in Phillip's ear "do you think I should mention that to our guests?". Phillip agrees saying "yes, that would be a good idea".
So the queen leans over to the the King of Tonga and says: "please do excuse me, I'm very embarrassed about that", to which the king of Tonga replies, "that's ok ma'am, I thought it was the horse".