Prince Harry's resentment towards 'calculated' Prince William: 'Made him feel like the spare at all times'

The rift between Prince Harry and Prince William was a long time coming, according to a royal expert, who says Harry feels "resentment" towards his brother and believes he behaved in a "calculated" way to ensure he was "the spare."

Tina Brown, a royal expert and author of the book The Palace Papers told LBC News in the UK the Prince of Wales and DUke of Sussex are "totally estranged" and unlikely to reconcile.

"The longer Harry dwells on what happened in his life, the more he feels resentment against William," Brown explained.

READ MORE: Rumoured couple Anna Wintour and Bill Nighy deny romance rumours

"He feels, I think, that William was even more calculated, essentially, in making him the number two, making him the spare, and feel like the spare at all times."

While the brothers will cross paths in some way at King Charles' coronation on May 6, Brown says that will be minimal, if at all.

"So there's no contact between them, I'm told. I think Charles wants to have some kind of rapprochement," she continued.

"But I think it's going to take years... it never happened between George VI and the Duke of Windsor, it just got worse.

READ MORE: British broadcasters reluctant to evacuate Buckingham Palace

"Alienations tend to get worse as time goes by, rather than better".

Prince Harry, 38, confirmed he will be attending his father's coronation in the UK alone, with wife Meghan and the couple's children Archie, three, and Lilibet, one, remaining in the US.

Harry is expected to fly in and out of the UK in 24 hours to make it back home in time to join celebrations for Archie's fourth birthday, which also falls on May 6.

READ MORE: The best portable heaters to keep you warm in winter

While exact details of Prince Harry's travel plans have not been made public due to security reasons, it's likely he will arrive in London on Friday.

It's believed he'll stay at Frogmore Cottage, potentially for the last time before handing over the keys, on Friday evening.

That same night, he could potentially join the other royals at Buckingham Palace for a reception for VIPs, dignitaries and foreign royalty.

Harry will then attend the coronation of his father at Westminster Abbey at 11am on Saturday.