Dickie Arbiter, who was the Queen's press secretary for several years, says the system is there to protect the Royal Family.
Neither Meghan and Harry or Kate and William were in the procession at the Commonwealth Day service.
The duke visited Abbey Road studios where Jon Bon Jovi is recording Unbroken which will be the Invictus Games song.
Ayesha Hazarika, who introduced Harry for his travel conference, said the royal doesn't seem 'wracked with anxiety'.
The Duchess was pictured visiting Mayhew, an animal welfare charity of which she is patron.
'I know I haven’t always gotten it right, but as far as this goes, there really was no other option.'
It is not yet known whether the Duke and Duchess of Sussex will stay on as patrons of the charities and organisations they represent.
Today’s engagement will see Prince Harry host draws for the men's, women's and wheelchair tournaments of the Rugby League World Cup 2021.
“I was a bit disappointed that Harry and Meghan have decided not to spend Christmas with the Queen this year."
It comes in the wake of the Duke and Duchess of Sussex’s private jet row in the summer of this year.
And Meghan Markle says she'll dress baby Archie in an England babygro as they cheer on from Frogmore cottage.