With his powdered wig and poker face, Washington looks so standoffish in his painted portraits that historians were naturally delighted to discover a touch of human frailty: While engaged to Martha, it now seems possible that he was boffing his best friend’s wife, the foxy Sally Fairfax. Others, more cautiously, say it was only a crush.

The evidence rests on two mysterious letters sent in September 1758, when George was a social-climbing, 26-year-old farmer-turned-army colonel writing from the front lines of the French and Indian War, and Sally was the belle of Virginia, a pretty, sophisticated and flirtatious minx two years his senior. George had met Sally several years earlier, when she married his Anglophile neighbor, G. W. Fairfax, in Mount Vernon, Virginia. The Washingtons and Fairfaxes were old family friends, so young George spent many nights playing cards, dancing, and enjoying amateur theatricals at the luxurious Fairfax mansion. Then,… More…