Harry, the younger son of King Charles, co-founded Sentebale in 2006 in honour of his late mother Princess Diana.
He left it, along with co-founder Prince Seeiso of Lesotho and the board of trustees, following a dispute with chair Sophie Chandauka.
In an interview with Sky News that will be broadcast in full on Sunday, Chandauka said, referring to the way Harry resigned: "At some point on Tuesday, Prince Harry authorised the release of a damaging piece of news to the outside world without informing me or my country directors, or my executive director".
"And can you imagine what that attack has done for me, on me and the 540 individuals in the Sentebale organisations and their family," she said.
"That is an example of harassment and bullying at scale."
Representatives for Harry and his wife Meghan did not immediately respond to a request for comment on the allegations.
Sky News said the couple declined to offer any formal response to the interview.
Harry and Seeiso said in a joint statement on Wednesday that it was "devastating" that the relationship between the charity's trustees and Chandauka had broken beyond repair.
Chandauka has previously said Sentebale was beset by "poor governance, weak executive management, abuse of power, bullying, harassment, misogyny (and) misogynoir".
In an interview with the Financial Times published on Saturday, she said she was asked by Harry's team to protect Meghan after negative media coverage, which she refused to do.
She also said the way Sentebale was run "was no longer appropriate in 2023 in a post-Black Lives Matter world ... funders were asking for locally-led initiatives".
Harry and Seeiso said on Wednesday that the trustees acted in the charity's best interests in asking Chandauka to step down, but in turn she sued Sentebale to remain in her position.
