William and Kate in Boston after palace race row

The Prince and Princess of Wales have visited Boston in a tour of the US that has been overshadowed by a row over racism in the UK.

The royal couple are in the US to hand out awards for their Earthshot Prize.

But it comes as the prince's godmother, Lady Susan Hussey, resigned after she repeatedly asked Ngozi Fulani, a black British charity boss, where she was "really" from.

A spokesperson for Prince William said "racism has no place in our society".

Lady Hussey, a close confidante of the late Queen and her longest-serving lady-in-waiting, has apologised and resigned since the incident.

Ngozi Fulani, who founded domestic violence charity Sistah Space, was repeatedly questioned by Lady Hussey about her background at an event to support the Queen Consort's campaign against domestic violence at Buckingham Palace on Tuesday.

Ms Fulani responded three times that she was British.

"I'm thinking to myself, is it that she - because she keeps asking me the same question - could it be that she can't hear me well? Because you have to consider so many things when you're talking to someone who may be older than you...," she told BBC Radio 4's Today programme.

"But it soon dawned on me very quickly that this was nothing to do with her capacity to understand, but this is her trying to make me really denounce my British citizenship."

Ms Fulani said it had led her to question how a situation like this could happen in a space "supposed to protect women against all kinds of violence".

"Although it's not physical violence, it is an abuse," she said.

Shortly after the prince arrived in the US, his spokesperson sought to distance Prince William from his godmother's remarks.

"The comments were unacceptable, and it is right that the individual has stepped aside with immediate effect," they said.

Ms Fulani said she did not want to see Lady Hussey "vilified".

It is far from the ideal start to this visit.

Events at Buckingham Palace have been embarrassing and distracting.

The focus for the Prince and Princess of Wales in the United States was due to be environmental innovation, optimism about the future and meetings with a wide range of communities in Boston.

Before the royal couple had even arrived in the city, their spokesperson had issued a strongly worded statement condemning racism and supporting the decision of Prince William's godmother, Lady Susan Hussey, to step aside.

Timing mattered here. Condemnation of her remarks from both Buckingham Palace and Kensington Palace was swift and unequivocal.

In issuing a statement at the very start of their American visit, the Prince and Princess of Wales have made their position and feelings on the matter explicitly clear - there is no place for this kind of comment and questioning within the royal household.

And all this just a few days before the Duke and Duchess of Sussex are due in New York to receive a human rights award from the Robert F Kennedy Foundation. Robert Kennedy's daughter, Kerry, says Harry and Meghan were chosen for the honour due to their "heroic stand" against "structural racism" within the royal family.

The royal couple launched the countdown to Friday's Earthshot Prize - which seeks to find and support innovative solutions to problems facing the planet - by lighting up Boston's landmarks in green on Wednesday.

Crowds stood in the rain to welcome William and Catherine to the city hall in Boston, home town of former US president John F Kennedy, on whose 'Moonshot' challenge the Earthshot challenge is based.

"Like President Kennedy, Catherine and I firmly believe that we all have it in ourselves to achieve great things, and that human beings have the ability to lead, innovate and problem-solve," Prince William told the crowd.

On his first overseas visit since the death of the Queen Elizabeth II, the prince said he wanted to thank the people of Boston for "their many tributes" to the late Queen.

"My grandmother was one of life's optimists. And so am I. That is why last year we launched the Earthshot Prize with the ambition to create a truly global platform to inspire hope and urgent optimism as we look to save the future of our planet," he said.

It comes after a planned trip to New York by the royal couple earlier this year was cancelled following the death of the Queen.

One of the guest speakers launching the Earthshot event, Reverend Mariama White-Hammond, gave a lecture on the legacy of colonialism and racism and "its deep connection to the degradation of land and our planet that we are all seeking to reverse".

At a basketball game attended by the Prince and Princess of Wales following the launch, some boos could be heard in the arena when the royal couple were introduced by a stadium announcer and shown on a big screen.

Five winners of the Earthshot Prize will be announced in Boston on Friday - each of whom will be given £1m ($1.2m) to develop their environmental projects.

Among the 15 finalists is a London start-up Notpla which makes packaging from seaweed and plants as an alternative to single-use plastic.

Prince William has described the people in the shortlist for the prize - now in its second year - as "innovators, leaders and visionaries".

The royal couple will also meet President Joe Biden over the course of their visit, the White House has said.