"The idea of putting out a statement which agrees that they can't use the word royal but contradicts the idea the monarchy can stop them using it," he said, "they're basically saying the royals can't stop them using it, but they won't be using it".
"It has been especially unnecessary to underline it in this way, especially as the agreement will be reviewed after a year.
"It simply empathises the division that we know that's there. The tone they've taken is that they are unhappy, they've made it clear every step of the way."
Fitzwilliams headed up the prestigious publication from 1975 to 2001 and arranged to meet many of its entrants.
Prince Charles' biographer Tom Bower said the public was "finally seeing Meghan's true nature and motives".
"Her comments about the Queen's decision smacks of spiteful fury," he said. "I fear it will get worse."
Bower detailed Prince Charle's scandal-ridden attempts to rehabilitate himself in his bestselling biography published two years ago.
Piers Morgan has also weighed into the royal debate, accusing Harry and Meghan of showing "staggering disrespect" to Harry's 93-year-old grandmother.
"The staggering disrespect these two keep showing to the Queen is outrageous," he said on Twitter.
"Who the hell do they think they are?"
The Daily Mail's Saturday Diary Editor, Richard Eden, said that the royal family's decision to strip Harry and Meghan of the brand "Sussex Royal" would have come as a "huge blow" to the pair as it was "central to their future plans".
'"And it's embarrassing for them, as the plans they originally outlined are so different from what they have been forced to accept," he said.
"However, Harry doesn't need to use the word 'royal' as everyone knows he is the brother of our future king.
"He and Meghan will want to keep relations with the rest of the Royal Family as friendly as possible, so will comply with Buckingham Palace's demands."
In their sour statement released yesterday and published to Instagram the Duke and Duchess said: "While there is not any jurisdiction by The Monarchy or Cabinet Office over the use of the word 'Royal' overseas, The Duke and Duchess of Sussex do not intend to use 'Sussex Royal' or any iteration of the word 'Royal' in any territory (either within the UK or otherwise) when the transition occurs Spring 2020."
In terse words the couple also outlined how they "will continue to require effective security to protect them and their son".
"The preference of The Duke and Duchess of Sussex was to continue to represent and support Her Majesty The Queen albeit in a more limited capacity, while not drawing on the sovereign grant," they said.
The Duke and Duchess quit the royal family this year to start a new life together in Canada with their son Archie.
They have since made an estimated £750,000 for speaking at an event for bank JP Morgan, and have also faced criticism for allegedly sending their security guards to fetch ethical meals for them.
The sixth-in-line to the throne and his wife are expected to rake in millions as they launch their life outside the royal family on March 31.
They have been working on a mental health series with Oprah Winfrey and Apple TV, and are said to be considering a venture with Goldman Sachs.
