Journalist Angela Levin, who spent a year with Prince Harry while writing his biography, claimed the royal is "absolutely furious" about being ignored on their recent trip to the UK.
Ms Levin alleged that Harry didn't think to check brother Prince William's diary before departing from his California home, with wife Meghan and children Lilibet, one, and Archie, three.
It is understood that the brothers did not meet privately during the four-day celebrations for their grandmother's 70-year reign.
The Queen did meet with the Sussexes during their visit, but is said to have declined a photo opportunity with her granddaughter Lilibet during her first birthday celebrations.
The couple reportedly met with Charles and Camilla in private.
Ms Levin said:" I think he would have been very upset that he was largely ignored.
"He still feels he's owed an apology."
Prince Harry has demanded an apology from the Royal Family over the treatment of his family during the jubilee celebrations
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In an interview with The Sun Online, Ms Levin continued: "But he's the one who should apologise.
"He said during the Oprah interview that Charles and William were trapped, he said he'd been cut off by his father.
"You can't just go around being rude about people and expecting them to open their hearts to you again."
On Saturday, Harry and Meghan held a first birthday party for Lilibet at Frogmore Cottage, inviting close members of the Royal Family, including Zara and Mike TIndall's, children for party games and picnic food.
The couple were seated in the second row of the congregation of St Paul's
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Ms Levin added: "Allegedly, they asked Kate and William and the children to the party.
""However, they didn't take the trouble of finding out the Cambridges would be in Wales on the morning, and coming back to get ready for the Jubilee concert in the afternoon, so they couldn't go."
The Sussexes made one public appearance over the Jubilee celebrations, attending the Service of Thanksgiving at St Paul's Cathedral on Thursday.
They were seated in the second row of the congregation, across the aisle from the Duke and Duchess of Cornwall and Kate and William.
Harry's facial expressions and body language showcased his emotions during the event, and the couple were swiftly whisked away following the service to their Windsor residence Frogmore Cottage.
Ms Levin added: "The thing that really stood out for me on that day was Harry's anger – he wears his emotions on his face and he looked absolutely furious.
"I think it's quite interesting really – he could have been feeling lots of things.
"I don't know whether he had a wave of feeling at what he had given up.
"He is self-destructive and might regret what he has lost.
"Or maybe he was recalling bad memories and was just wishing he hadn't come at all."
The journalist emphasised how Harry should have made a trip prior to the Jubilee at a "quieter time" to make peace with his brother.
"You can't expect to be close if you just have a few minutes," she said.
In an interview with GB News yesterday Ms Levin emphasised how the Palace "made sure that Harry and Meghan realised the Royal Family has moved on".
