Harry's expected to attend Charles' ceremony on May 6 in London.
Royal correspondent Omid Scobie, author of the Harry and Meghan Markle biography Finding Freedom, tells ET that this trip back to London will be the first time Harry comes face-to-face with his family since the release of his memoir, but it most certainly won't be the first time that he's spoken with some of them.
"Harry's had several conversations with his father over the months since the release of the book, largely about the coronation itself and, of course, matters to do with Frogmore Cottage, which the couple will no longer have the keys for any week now," Scobie says.
Harry and Meghan were evicted from the cottage just a couple of months ago, with the king's disgraced brother, Prince Andrew, set to live there. Harry and Meghan have until early summer to vacate the property.
As for Harry and William's relationship, Scobie says nothing's changed in the matter. It's still as icy as ever.
"It's been stone-cold silence between the two brothers and that's continued since the queen's funeral through the release of the Netflix series, the book, and, of course, now this trip to London," the royal correspondent says, "and I don't think things will change."
Just days ago, William's very important role in his father's coronation was announced. According to the Liturgy of the Coronation Service, the Prince of Wales will pledge his loyalty and allegiance to the king during the ceremony at Westminster Abbey on May 6. William, 40, the heir to the throne, will kneel before his father -- after he is officially crowned -- place his hands between the king's and recite the words also known as the Homage of Royal Blood.
"I, William, Prince of Wales, pledge my loyalty to you and faith and truth I will bear unto you, as your liege man of life and limb. So help me God."
William is the only royal who will honor the king in this way during the ceremony. A role for Harry was not listed.
So, why make the trek when things remain icy with the family and no apparent role at the ceremony? Scobie, whose second royal book ENDGAME: Inside the Royal Family and the Monarchy's Fight for Survival drops Aug. 1, says Harry's presence alone is significant.
"He's the son of King Charles III, a man who he still respects and has a great adoration for despite the fractures in their relationship," said Scobie of Harry, who is attending without Meghan or their children. "But he's also fifth in line to the throne and a Counselor of State. So, it's important for him to be here in a constitutional position, regardless of how he feels about his family. But I hear from sources, he is looking forward to being a part of this moment despite things of the past that have happened."
That being said, Harry's trip to London will be done "in a flash."
"People around him are working as hard as they can to find the quickest way into the country and the quickest way out," Scobie says. "He's really only coming here for the ceremony, so any hopes for reconciliatory moments or private heart to heart between father and son or any of his family members, I think they'll be waiting for another time."