The UK's Prince and Princess of Wales were subjected to booing as they attended a basketball game in Boston at the end of the first day of their visit to the US.
Kate and William stood for the national anthem The Star Spangled Banner before the NBA game between the Boston Celtics and Miami Heat.
However, boos were heard around the arena when they were introduced by a stadium announcer and shown on the big screen.
Other fans in the crowd could be heard loudly cheering "USA, USA" when the prince and princess appeared on the screens in the centre above the court.
The Boston Celtics' name was inspired by the Original Celtics, a well-known basketball team that had been created by Irish immigrants in New York earlier in the 20th century, before folding in 1930.
The three-day trip to Boston has been overshadowed by the growing race row engulfing the future king's godmother, which has left the British monarchy accused of being institutionally racist.
Lady Susan Hussey has resigned from her role in the royal household and apologised yesterday.
She had repeatedly questioned a prominent black British-born domestic abuse charity boss about where she "really came from" during a Buckingham Palace reception.
The prince is understood to agree it was right for Ms Hussey to step down from her honorary role as one of three Ladies of the Household.
A Kensington Palace spokesman told reporters in the US ahead of the three-day trip to Boston: "Racism has no place in our society."
At the start of the basketball game last night the prince and princess were seen watching intently as the Celtics raced into an early lead.
They sat courtside alongside Massachusetts Governor-Elect, Maura Healey, Celtics Legend Thomas "Satch" Sanders, and the team's two principal owners and their wives.
After the second quarter with the game tied 47 all William and Kate watched as the Celtics honoured their long standing tradition of recognising a "Hero Among Us", heralding individuals working to positively impact the community.
Ollie Perrault, a 15-year-old climate activist, now the founder and director of Youth Climate Action Now, met the royal pair after being cheered by the local crowd for her work as a leading member of the Youth Climate Leadership Program since she was 11.