Prince Harry and Meghan Markle could regret choosing not to attend the memorial service for Prince Philip, according to royal experts.
The Duke and Duchess of Sussex will not be present at Westminster Abbey for the poignant event later this morning.
The Queen is said to be likely "very upset" by the snub but can't change her grandson's mind.
The Duke of Edinburgh passed away on April 9, 2021, at Windsor Castle at the age of 99.
It comes as Harry - who lives with Meghan and their two children Archie, two, and Lilibet, nine months, in Montecito, California - is currently pursuing a legal challenge against the Home Office.
He has been told by the government department he is no longer eligible for the same degree of personal protective security when visiting the UK after he stepped down as a working royal in 2020.
The Duke, 37, was last on home shores in July to unveil the statue of his late mum, Princess Diana, alongside brother Prince William.
But since then, he has said he doesn't feel safe bringing his family over to the UK without the huge extra security other members of the Firm receive from the Met Police.
He has offered to pay for it himself, but has been told it is not feasible.
Harry is the only top-level royal not attending today's service, which begins at 10.30am.
Royal author Phil Dampier told MailOnline : "It's very sad that Harry and Meghan won't be at Prince Philip's memorial service and I think one day Harry might regret it.
"He has said that he doesn't feel safe without Scotland Yard security but to me that sounds like an excuse not to come back to the UK and indicates the rift with his blood family is still bad.
'Harry was always very fond of his grandfather and was deeply honoured when he took over from him as Captain General of the Royal Marines, but sadly that didn't last long."
Mr Dampier said Harry's fondness for his beloved grandfather makes his snub "all the more mystifying and strange" - and will likely be very upsetting for the Queen.
He added that there "must now be great doubts" about whether he will attend any of her Platinum Jubilee celebrations later this summer.
Royal commentator Victoria Arbiter, meanwhile, agrees Harry could regret his decision, and that members of the Firm "very rarely say no" to such occasions.
She told Nine.com.au : "There's likely to be a strong turnout from extended members of the family, each of whom will be keen to provide the Queen a sense of unity as she publicly mourns her husband once again.
"Though she's never been one to hold a grudge, surely it would be better for Prince Harry to make his peace now as opposed to living with a lifetime filled with potential regret. There are no second chances for occasions such as these."
Royal expert Ingrid Seward told the Mirror Prince Philip would be extremely angry that his grandson is skipping the service.
In contrast to the Queen, who has had to cancel other public appearances as she recovers from a bad back was "determined" to attend the service "however hard it is for her to get there", said Ms Seward.
"She knows he would expect it as much as she knows he [Philip] would be angry and disappointed Prince Harry has chosen not to go."
Royal commentator Kinsey Schofield told Express.co.uk that the memorial is an event "where he would have that security that he's asking for, so it feels like this is just him trying to make a statement".
Royal author Robert Jobson told US Weekly : "It's disappointing [because there] doesn't appear to be any serious reason why he [Harry] can't be there. He's going to Holland for the Invictus Games shortly afterwards."
