An empty stone coffin now to be found in St Mary's and St Nicholas's Church, Beaumaris, has long been considered to be that of Joan. The panel above the coffin is inscribed: "This plain sarcophagus, (once dignified as having contained the remains of Joan, daughter of King John, and consort of Llewelyn ap Iowerth, Prince of North Wales, who died in the year 1237), having been conveyed from the Friary of Llanfaes, and alas, used for many years as a horsewatering trough, was rescued from such an indignity and placed here for preservation as well as to excite serious meditation on the transitory nature of all sublunary distinctions. By Thomas James Warren Bulkeley, Viscount Bulkeley, Oct 1808"
