That’s according to the royal editor of the Daily Mirror, Russell Myers, who made the comments on UK television overnight.
The Duke and Duchess of Sussex have filmed a wide-ranging interview with the queen of American television, to air on March 7.
It will begin with a chat with the duchess before Prince Harry joins his wife and Winfrey in the 90-minute special.
The interview will mark the first time the couple has spoken in detail about their royal exit, and will be broadcast just weeks before the one-year anniversary of the so-called ‘Megxit’ arrangement being finalised.
But the Queen, and palace aides, were reportedly left in the dark about the interview, with the announcement coming from US network CBS.
“If you’re going to set off a nuclear bomb like this, doing a huge interview which will no doubt garner attention across global networks, the decent thing to do would be to tell the Queen, tell your granny you’re going to do it,” Myers told British morning television host program Lorraine.
“We know they have gone alone and set this path for themselves, the very fact is they are separate from the royal family now.”
As non-working members of the British royal family, Harry and Meghan were – technically – not expected to inform The Firm of their plans.
But Myers says some decency should have applied in the couple’s thought process.
“Palace aides were saying, ‘Look, they didn’t need to tell us if they didn’t want to’ but one would think there is common courtesy,” he said.
“Whenever royals do these big tell-all interviews, they have disastrous consequences. Look at Prince Andrew recently, further back in the 90s with Diana and Charles, we’re still talking about them now.”
The last royal Winfrey interviewed was Sarah, the Duchess of York, in 2010, when she spoke in detail about her lifelong personal struggles, debt and quest for perfection.
It came just weeks after the duchess was caught in an undercover hidden camera sting by a British tabloid, trying to sell access to her ex-husband Prince Andrew.