In the summer of 1649, following his father’s (Charles I) execution, Charles left The Hague and travelled to Paris to comfort his mother and sister. This visit established a close bond between Charles and Henriette Anne. The earliest surviving letter between Henriette Anne and Charles dates from late 1659. Thereafter the siblings wrote to each other almost every week in an informal and affectionate tone. Charles valued his sister’s opinion on matters of state, and, as the years progressed, the content of their letters became deeply political with the negotiations for an alliance between France and Britain taking centre stage.