Prince William, Kate Middleton at Celtics Game as 'Harry & Meghan' Trailer Drops

Prince William and Kate Middleton spent their first night in the U.S. at a Celtics game, as one Royal controversy has exploded and another is on the way.

The Duke & Duchess of Cambridge were front and center at the Celtics game Wednesday night against the Miami Heat -- they're in town for Friday's Earthshot Prize Awards Ceremony ... created by William to find solutions for global warming.

When they popped up on the jumbotron, there was a smattering ... maybe more than a smattering of boos. Now we all know that's the way Boston fans roll, but their appearance came just hours after William's Godmother, Lady Susan Hussey, stepped down from her Royal duties after asking some racist questions at an event.

And, then there's Harry and Meghan ... hours after the game Netflix dropped a trailer for their upcoming documentary, and it's clear as day they're going after the fam. Harry says, "No one sees what goes on behind closed doors. I had to do everything I could to protect my family."

The two brothers will NOT see each other during William's 3-day stay in the States. So much for a reconciliation after the Queen's death.