Lady Colin Campbell clashed with Phillip Schofield while promoting her new book about Prince harry and Meghan Markle on This Morning.
The royal expert, who came to prominence with her bestselling biography of Princess Diana entitled "Diana in Private: The Princess nobody knows", called Schofield "ignorant".
Her new book "Meghan and Harry: The real story" is described as a "behind the scenes" look into the couple's decision to step back as senior royals.
The clash occurred after Schofield referenced Lady Colin Campbell's Diana book during the interview, calling it "gossip".
Schofield told her: "I’d be surprised any of the royals would want to get involved with more gossip after your Princess Diana book."
In response Lady Colin Campbell hit out at the TV presenter calling him "ignorant".
She said: "It's history in the making. That shows how ignorant you are if I may point out.
"My Diana biography was named the most believable by People Magazine and had it not been for that biography, Diana would have thrown Prince Charles to the wolves."
Lady Colin Campbell added that there was nothing "tawdry or undignified about the truth".
Schofield ended the interview by calling Lady Colin Campbell's behaviour "patronising".
“It’s been fascinating, if a little patronising", he said.
"Thank you for joining us today.”
