The King’s decision to publish his full tax returns marks one of the most significant acts of financial transparency ever undertaken by a British monarch.While the late Queen Elizabeth voluntarily paid tax, none has publicly revealed the amount they contribute to the Treasury.In doing so, the King is taking a huge step towards modernising the monarchy and aligning it with contemporary expectations of accountability.Buckingham Palace's explanation that the move demonstrates the institution's determination to "continue to modernise and evolve" reflects a reality that has shaped Charles's reign from the outset.‌However, perhaps this is not surprising at all.As Prince of Wales, Charles followed this exact same practice and since ascending the throne in 2022, the King has sought to present a monarchy that is leaner, more transparent and more responsive to public concerns.Releasing his tax returns is perhaps the clearest expression yet of that ambition.Without question, it also puts into sharp focus the controversial decision by Prince William to choose not to publish his tax affairs when he inherited the Duchy of Cornwall estate from his father.‌While William has made great strides in promoting a new direction, choosing to identify land for social housing on the Duchy and cancel extortionate rents for schools on his land, he surely now must perform a u-turn on his decision to keep his tax affairs private.