They met Mayor Michelle Wu in Boston City Hall and attended a Celtics game, where they were pictured hand-in-hand with William's hand on Kate's knee.
Their excursion was best at the Earthshot Prize ceremony. On the "green carpet," William held Kate's back.
The couple has been married for almost 12 years and has three children.
Lady Susan Hussey, the prince's godmother, resigned as a "Lady of the Household" after being accused of racially offensive chat with a charity leader at a Buckingham Palace reception.