Esmeralda Pye was the daughter of Queen Etheldredda and the sister of Marcellus Pye. She had two infant sisters. Esmeralda was a quite lonely princess and she favored the visits of her brother Marcellus. Sir Hereward, a ghost knight, guarded her rooms. Esmeralda appeared in the third book of the Septimus Heap series, Physik. Marcellus had lied and said that Esmeralda had drowned in the river. Therefore, Jenna Heap, who looked a lot like Esmeralda, was mistaken to be the Princess by the Palace guards when she went through time to find Septimus, who had been trapped shortly before by Queen Etheldredda and Marcellus. Esmeralda kept a diary under her bed mattress where she wrote about Marcellus's visits and the events that were going around her. After Jenna met her and explained her journey in Keepers Cottage, Esmeralda stayed there away from her mother, Queen Etheldredda. In the epilogue of Physik, it is stated that she had two daughters, Princesses Daisy and Boo, who both became Queens in succession; Daisy was said to have had five sons but no daughters, and the crown had to pass to the nearest living Princess.