Harry and Meghan have also moved home to the royal family's Windsor estate, west of London, from a cottage in the grounds of Kensington Palace where William and Kate, the Duke and Duchess of Cambridge, live.
She added that the Princes have "gone their separate ways", but that Prince Harry "is in his mid-thirties and I think it is perfectly OK for him to be independent of his brother".
The comment simply read "Happy Birthday to the Duke of Cambridge!"
All, except for the Duke and Duchess of Sussex, who, in the early morning they were yet to post anything on their official account.
This formal statement comes in great contrast to the gushing photo tributes they posted for the Queen and Philip, and even the warm birthday messages they wrote for Prince Louis and Princess Charlotte.
And one royal expert believes this move was "pretty rude" by both Harry and Meghan.
Trump eyes more Iran sanctions; military action still on table
The digital response reportedly targeted an Iran-based spy group that was involved in last week's mine attacks on cargo ships. Israeli military analysts are afraid that a weak U.S. attack on Iran could provoke an Iranian attack on Israeli interests.
Ingrid Seward, the editor in chief at Majesty Magazine, said the thought it was "pretty rude" that the Sussexes didn't do more to mark the day.
"That is the trouble with Instagram, it becomes your slave".
Most recently, Harry and Meghan made a decision to leave the joint charity foundation they ran with William and Kate.
Harry and Meghan, the Duke and Duchess of Sussex, will set up their own charitable foundation later this year, the palace said, while the decade-old Royal Foundation will remain the main philanthropic vehicle for heir-to-the-throne William and Kate.
"It is clear that Meghan and Harry were initially prepared to slot in under the wing of William and Kate but that's not how they feel a year on".
But Harry and Meghan have split from the organisation, and intend to establish their own charity.