Four days after saying her "I Do" to Prince Harry, Meghan Markle has already started off on the wrong foot with her British royal in-laws. 

Author Lady Colin Campbell talked to The Daily Star revealed that the Duchess of Sussex was the topic of conversation at their house on Wednesday, May 23, 2018, during the time she had done something "astonishing" at Prince Charles' 70th birthday party and the first-ever garden party at Buckingham Palace.

Lady Campbell is best known for her books such as "Diana in Private: The Princess Nobody" and for starring in "I'm A Celebrity Get Me Out of Here."

And that's when tensions began. It was the first royal blunder of Meghan Markle, and it reportedly disappointed the royal family.

"I can't repeat it exactly, it's in the book, but what I can say is, something happened at the very first garden party at Buckingham Palace."

"We were all absolutely gobsmacked and astonished; we all thought this doesn't bode well."

She revealed how the entire British royal family wanted Meghan Markle to succeed, but there were already "warning signs" that emerged days after her wedding to Prince Harry.

"It was not a good harbinger, we were all hoping against hope the information was wrong, but of course, it was accurate." 

Photos from that day showed the Duchess of Sussex looking cheerful and smiling with the Duke of Sussex and her in-laws, Prince Charles and Camilla. 

Lady Campbell suggested that whatever allegedly went wrong that day was the reason for the reported "rift" between Meghan Markle and the royal family, that eventually seeing the Duke and Duchess of Sussex leaving the royal family.

Everybody Was Rooting for Meghan Markle to Be a Success

Her book, "Meghan and Harry: The Real Story," is set for release this month and revealed that she started writing the book as somebody who was "positive and invested in" the Duchess of Sussex to become successful in her transition to Britain's famous family. 

Lady Campbell insists that in writing the book is not to drag her down.

"I knew the tremendous amount of hope the Royal Family invested in Meghan being a success," Lady Campbell continued, "Hundreds of millions of people of color were rooting for Meghan, I was rooting for Meghan, being a Jamaican, I was emotionally invested in Meghan's success."

"Virtually everybody I know, including my royal friends, the wider aristocracy, wanted Meghan to be a success."

Lady Campbell further said, "But it quickly became apparent the ride may not be as smooth as everybody had hoped it would be, and it would not be as quite as positive as everybody had hoped it would be." 

The New American Life of Meghan Markle and Prince Harry Now

After the announcement of their new foundation "Archewell" in April, The Telegraph that the public unveiling of their project is not on the cards until 2021 as they are also focusing their efforts toward the COVID-19 and Black Lives Matter movement. 

A source told the news website, "What's absolutely clear is that they want to get it right and there's no point in rushing. They are setting into a new life, a new era. This is about getting it right and making sure they can make the difference they want to make." 

Since moving to Los Angeles at the end of March, Meghan Markle hasn't seen or visited her mother because of the coronavirus lockdown orders. 

However, it was recently reported that the Duchess of Sussex had moved her mother, Doria Ragland, into their $18 million rented mansion. 

A source told The Sun, "Doria has her own quarters, and while a few of Harry's chums have been ribbing him about living with his mother-in-law, he has a brilliant relationship with her." 

Another source told the tabloid that Meghan Markle wants her 63-year-old mother as close as she is her "rock" and doesn't "trust" people outside of their immediate circle of family and friends.  

READ MORE: Meghan Markle True Identity: BFF Jessica Mulroney Manipulated to Lie About Duchess?