AP and Charlotte performed flying changes, piaffe, passage and extended trot for the Cheltenham crowd.
“AP was amazing. Obviously, dressage is completely different to race-riding and he coped really well,” said Charlotte.
AP added: “I think that’s a bit flattering! It’s a different way of riding to everything I was taught. Everything you do as a jockey you wouldn’t do as a dressage rider, but it was a good experience and I’m very lucky to have someone like Charlotte to show me what to do.
“But I think it’s time to retire from that as well!”
AP was on the nine-year-old owned by Anna Kohn and Carl Hester, while Charlotte rode Pro-Set, owned by Carl Hester and Karen Shepherd.
Pro-Set, a licensed stallion by Jet Set D x Flemmingh, finished second to Barolo in the Hartpury competition.
“It was Yogi’s [Breisner] idea that it might be nice to get AP to have a sit on a dressage horse and see what he can do,” Carl Hester told H&H.
“The first thing he needs to do is learn to slow down and shift his weight in a different way.”
Yogi Breisner, the British eventing team’s chef d’equipe added on watching him today: “I don’t think AP has cantered this slowly in his life before.”
Countryside Day at The Open is in aid of the Countryside Alliance and the British Olympic Team.
Earlier in the day The Princess Royal officially opened the new £45m grandstand that bears her name.