Meghan Markle accused Buckingham Palace of “perpetuating falsehoods” about her and Prince Harry, suggesting the couple will not be silent in telling their story about their time as working royals.
In a second teaser clip of an upcoming interview with Oprah Winfrey, Meghan was asked how she felt about the palace hearing her “speak her truth today”.
The duchess responded: "I don't know how they could expect that after all of this time we would still just be silent, if there is an active role that The Firm is playing in perpetuating falsehoods about us.
"And if that comes with risk of losing things, I mean, there's a lot that's been lost already.”
The Firm is the name that the British royal family sometimes uses to describe itself but it could also apply to staff in the wider household.
The clip was recorded before Buckingham Palace said on Wednesday it would investigate allegations of bullying made against the duchess by former royal staff.
A report in The Times claimed an aide to Harry and Meghan raised a complaint in October 2018 alleging that Meghan had reduced some of her assistants to tears and treated others so badly that they had quit.
The paper said Prince Harry had urged the aide, who has now left their staff, to drop the complaint, and it never progressed.
In a highly unusual statement, the palace said it was "clearly very concerned about allegations in The Times".
"Accordingly our HR team will look into the circumstances outlined in the article," Buckingham Palace said.
"Members of staff involved at the time, including those who have left the Household, will be invited to participate to see if lessons can be learned."
The Royal Household will not tolerate bullying or harassment in the workplace, it added.
A spokesman for the duchess said that she was "saddened by this latest attack on her character, particularly as someone who has been the target of bullying herself and is deeply committed to supporting those who have experienced pain and trauma".
"She is determined to continue her work building compassion around the world and will keep striving to set an example for doing what is right and doing what is good."
Harry and Meghan, who married in May 2018, stepped back from their official duties in March last year to forge new careers and a financially independent life in California.
That decision was confirmed last month, when they also handed over all their royal patronages.
They said their move was fuelled in part by intense press intrusion, however, Meghan had also previously indicated that she felt she did not have the full support of the royal family.
In court documents submitted as part of her successful privacy action against the Mail on Sunday, her lawyers said she had felt "unprotected" while she was pregnant with their son Archie.