The royalty books that were bestsellers in the past two months, based on sales made through the Royalty.nu site and its companion blogs:
The Historical Atlas of Dynasties and Royal Houses by Jeremy Harwood. Starts with the birth of monarchy in the ancient Middle East and ends with coverage of modern royal houses and ruling dynasties.
All the King's Cooks by Peter Brears. The massive kitchens at Hampton Court were built to supply the household of Henry VIII. This book dispels misconceptions about cooking and eating in Tudor England.
Mary Boleyn: The Mistress of Kings by Alison Weir. Biography of Anne Boleyn's sister, who was Henry VIII's mistress before he became involved with Anne.
The Last Days of Richard III by John Ashdown-Hill. A detailed exploration of the English king's last 150 days, his burial, and the construction of his tomb.
The Story of King Arthur and His Knights by Howard Pyle. A retelling of the Arthur legend for children. This edition is abridged; you can find an unabridged edition here (at least I think it's the unabridged version; Amazon makes it difficult to tell).