The pair are believed to have rowed over a wedding dress fitting and the outfit requirements for Kate’s daughter, Princess Charlotte.
A royal insider told the Sun: “If she has chosen to speak candidly about her time with Kate then the damage that could be done to the monarchy is vast.
“She has the power to lay bare just how bad things really were between her, Harry, William and Kate.”
The source also described the interview as “Meghan’s nuclear option”.
The interview is set to watched by millions of viewers across the globe, with American broadcaster’s CBS peaking interest in the show by teasing short clips from their pre-recorded chat.
Clips released this week have set the tone of the interview and anticipated the Duke and Duchess of Sussex have addressed both Megxit and their relationship with the Royal Family.
In a teaser released on Thursday, Oprah asked Meghan how she felt knowing the palace would watch her speaking her truth.
CBS announced in February the interview would cover a broad range of topics, from motherhood to Meghan and Harry’s hopes and plans for the future.
The chat has been split in two parts, with Meghan speaking first alone with Oprah before being joined by the Duke of Sussex.
Prince Harry is also expected to touch upon the death of his mother, Princess Diana.
In one of the first trailers released this week, the Duke seemed to draw a comparison between his royal exit and his mother, who was stripped of her title after the Waleses’ divorce in 1996.
He said: “I’m just really relieved and happy to be sitting here talking to you with my wife by my side.
“Because I can’t begin to imagine what it must have been like for her, going through this process by herself all those years ago.
“It’s been unbelievably tough for the two of us, but at least we have each other.”