Mulroney, 40, also responded with a heart emoji to a post by journalist Katie Couric about the dramatic decision by the Sussexes, with some believing that she was aware of their decision - unlike Queen Elizabeth II.
On Wednesday, the Duke and Duchess of Sussex caused shock across the world by announcing that they will quit the royal family and move to North America.
In a statement issued on their Instagram account with 10.1 million followers on Wednesday evening UK time, they said: "After many months of reflection and internal discussions, we have chosen to make a transition this year in starting to carve out a progressive new role within this institution."
They continued: "We intend to step back as 'senior' members of the Royal Family and work to become financially independent, while continuing to fully support Her Majesty The Queen. It is with your encouragement, particularly over the last few years, that we feel prepared to make this adjustment.
"We now plan to balance our time between the United Kingdom and North America, continuing to honour our duty to The Queen, the Commonwealth, and our patronages. This geographic balance will enable us to raise our son with an appreciation for the royal tradition into which he was born, while also providing our family with the space to focus on the next chapter, including the launch of our new charitable entity.
"We look forward to sharing the full details of this exciting next step in due course, as we continue to collaborate with Her Majesty The Queen, The Prince of Wales, The Duke of Cambridge and all relevant parties. Until then, please accept our deepest thanks for your continued support."
In an incredibly harsh, two-line statement, released shortly after Meghan and Harry's bombshell announcement, the BBC learnt that neither the Queen nor Prince Charles were consulted before making the announcement that they were stepping away.
"Discussions with The Duke and Duchess of Sussex are at an early stage. We understand their desire to take a different approach, but these are complicated issues that will take time to work through."
On top of this frankly blunt statement from the Royal Family, the BBC claims that Her Majesty was not consulted before Meghan and Harry issued their personal statement.
"BREAKING: BBC Understands that no other member of the Royal Family was consulted before Harry and Meghan issued their personal statement tonight, the Palace is understood to be 'disappointed'."