Mary Berry's Country House Secrets episode 3: In this edition, Mary Berry visits Powderham Castle in Devon, to spend time with the Earl and Countess of Devon and their two young children. Known as Charlie and AJ, the newest generation of one of Britain's oldest families are taking up the challenge of running a great stately home, reinventing the castle and the Earldom for the 21st century.       Mary's time with the family reveals stories of romance and…