The late Queen’s lady in waiting has resigned and apologised after she made “unacceptable and deeply regrettable comments” by asking a prominent Black advocate for survivors of domestic abuse where she “really came from”.

Buckingham Palace said it took the incident, at the Queen Consort’s reception on violence against women on Tuesday, “extremely seriously” and had investigated immediately.

A source confirmed to the PA news agency that the person who made the remarks was Lady Susan Hussey, who served as Elizabeth II’s lady in waiting for more than 60 years and is a godmother to the Prince of Wales.

William is understood to agree it was right for Lady Susan to resign, with a Kensington Palace spokesman telling reporters in the US ahead of the Waleses’ trip to Boston: “Racism has no place in our society.

“The comments were unacceptable, and it is right that the individual has stepped aside with immediate effect.”

The Kensington Palace spokesman said he spoke to William before he boarded his commercial flight to the US with the princess, with the couple due to arrive at lunchtime local time on Wednesday for their first overseas visit since the Queen’s death.

Ngozi Fulani, chief executive of Sistah Space, in Hackney, detailed the conversation on Twitter, describing it as a “violation” and said the experience will “never leave me”.

She named the member of the palace household only as Lady SH, but the Palace refused to confirm who it was.

Lady Susan, 83, who was invited to and on duty at the reception, has now stepped down from her honorary role as one of three Ladies of the Household, to which she was newly appointed to help the King at formal occasions.

Charles, who acceded to the throne less than three months ago, and Camilla have been made aware of the situation, the Palace said.

Ms Fulani said she was challenged when she said her charity was based in Hackney, with “Lady SH” saying: “No, what part of Africa are YOU from?”

The Palace said in a statement: “In this instance, unacceptable and deeply regrettable comments have been made. We have reached out to Ngozi Fulani on this matter, and are inviting her to discuss all elements of her experience in person if she wishes.

“In the meantime, the individual concerned would like to express her profound apologies for the hurt caused and has stepped aside from her honorary role with immediate effect.

“All members of the Household are being reminded of the diversity and inclusivity policies which they are required to uphold at all times.”

Mandu Reid, leader of the Women’s Equality Party, who was next to Ms Fulani and witnessed the exchange, told the PA news agency they were treated like “trespassers”.

Ms Reid said: “We really felt ‘oh, OK, we’re being treated almost like trespassers in this place.

“‘We’re not being treated as if we belong, we’re not being embraced as if we are British.'”

She described the conversation as “grim” and like an “interrogation”, adding: “She was really persistent. She didn’t take Ngozi’s answers at face value.”

Ms Fulani detailed the encounter, which happened 10 minutes after she arrived in the Palace’s Picture Gallery, on social media, which included the remarks: “’Where are you from?’

“Me: ‘Here, UK’. ‘No, but what nationality are you?’ Me: ‘I am born here and am British.’ ‘No, but where do you really come from, where do your people come from?’ Me: “My people”, lady, what is this?’

“’Oh, I can see I am going to have a challenge getting you to say where you’re from.’”

Ms Fulani, who founded Sistah Space in 2015 to provide specialist support for African and Caribbean heritage women affected by abuse, wrote: “Mixed feelings about yesterday’s visit to Buckingham Palace.

“10 mins after arriving, a member of staff, Lady SH, approached me, moved my hair to see my name badge. The conversation below took place. The rest of the event is a blur.”

She thanked Ms Reid, the first person of colour to lead a national political party in British history, and Safe Lives chief executive Suzanne Jacob for their support on the day.

Responding to messages of support, Ms Fulani wrote: “Standing there in a room packed with people while this violation was taking place was so strange, especially as the event was about violence against women.

“That feeling of not knowing what to do, will NEVER leave me. Almost alone in a room full of advocates.”

She said it was a “struggle to stay in a space where you were violated”.

Ms Fulani outlined her distress at not being able to report the incident, saying she felt she could not tell Camilla.

“There was nobody to report it to. I couldn't report it to the Queen Consort, plus it was such a shock to me and the other 2 women, that we were stunned to temporary silence,” she wrote.

“I just stood at the edge of the room, smiled & engaged briefly with who spoke to me until I could leave.”

Ms Jacob tweeted it was “a horrible thing to happen, and in a space that should have been nothing but love and celebration” and said she would be raising it with the team who organised for them to be there.

The matter raises serious concerns for the Palace, where an unnamed royal was accused last year by the Duchess of Sussex of racism against her unborn son Archie.

Meghan, the first mixed race person to marry a senior royal for centuries, said during her Oprah interview that a royal – not the Queen nor the Duke of Edinburgh – expressed concerns with Harry about how dark Archie’s skin tone might be before he was born.

The Queen issued a statement saying that the issues raised would be dealt with privately as a family, but that “some recollections may vary”.

Sistah Space said they would not be naming the household member, adding: “We at Sistah Space would like to raise awareness about this issue rather than shame another individual.”

The Palace is understood to have reached out to Ms Fulani through one of the organisations with which she is aligned, but is yet to hear back, and hopes to work with her when she is ready, and to express apologies in person.