Harry and Charles had an awkward reunion during Prince Philip's funeral last month.
Harry had claimed his father and brother Prince William were "trapped" in the Royal Family during his interview with Oprah.
He also claimed Charles had used palace staff to carry out his parental responsibilities and that he had been cut off financially.
Charles was said to be "devastated", "despairing" and "deeply saddened" by Harry's comments in the interview.
Things got worse when Gayle King, the host of CBS's This Morning TV show and a friend of the Sussexes, revealed on air that calls between Harry and Charles had been "unproductive".