Harry was on hand in London for his father's official coronation on Saturday.
Harry was spotted entering the ceremony at Westminster Abbey on Saturday morning with his cousins, Princess Beatrice, Princes Eugenie, and Zara Tindall, as well as their respective spouses. He seemed in good spirits, smiling and chatting with Beatrice's husband, Edoardo Mapelli Mozzi, and sat with his family -- next to Eugenie's husband, Jack Brooksbank, and directly behind his aunt, Anne, Princess Royal.
Harry also joined the crown in reciting "God save King Charles" following his father's crowning and sang along to "God Save the King" as the monarchs processed out of Westminster Abbey. Following the ceremony, Harry was seen getting into a black BMW sedan, and departing Westminster Abbey.
ET spoke with royal expert Eloise Parker ahead of the May 6 ceremony, who shared some insights on what would likely go down between Harry and Charles during the coronation and it wasn't too far off from what viewers saw Saturday.
"I fully expect Prince Harry to be very much on the sidelines during this ceremony," Parker shared. "This ceremony is all about King Charles III and the Queen Consort, so I would expect even the Prince and Princess of Wales, William and Kate, will also be at the sidelines for this [event]."
It was recently revealed that Harry would be attending the coronation alone -- while his wife, Meghan Markle, and their two children -- Archie, who turns 4 on Saturday, and Lilibet, 1 -- will remain at home in California.
"[There was] some surprise that Harry is going alone, [but] not so much when you realize that it's his son, Archie's, birthday the very same day," Parker explained. "So Meghan is in fact going to be staying home in California to celebrate that birthday, which is perhaps quite convenient given the tensions between the two families right now."
A source told ET that Harry arrived in the U.K. on Friday morning, and was put up at his and Meghan's former home, Frogmore Cottage. He is expected to depart on Saturday following the coronation festivities. Meanwhile, ET has learned that Archie’s birthday celebration will be a small gathering with friends and family in Montecito.
While Harry attended solo -- and stayed out of the spotlight, for the most part --- Parker said it is "impossible to believe there's not gonna be some amount of tension, given just how intimate Harry's revelations were for the entire family in his book, Spare."
"I think this is the first time they're gonna be in person since the launch of that book," Parker added, noting that most of the attention will be on Charles on Saturday.
"There's going to be thousands of people around, all needing attention, Charles is gonna be very much at the center of that, so hopefully for Harry that's gonna take the emphasis off him," Parker shared. "I think most people are hoping that the father-son relationship will heal over time. Unfortunately, I just don't think the coronation is gonna be the event for that to happen."
"There's just gonna be too many people, too much pressure, and far too much going on," she said, adding that any eventual reconciliation is almost certainly going to come after the highly public royal event.
"Prince Harry will be back at the church. He's got a non-position," Morton said.
Speaking of the service, Morton said he's curious to see how Prince Harry interacts with his family members. "It will be interesting to see, when they walk down the aisle, whether Harry bows to his father and to the queen, whom he's not had many kind words for."
Like Parker, Morton noted that despite the family being fractured, the coronation is an official state ceremony, not a family reunion. So, he believes that the royal brothers will act "with majesty."
"This is a state occasion, not a family occasion. It's not a day for reconciliation, it's a day to confirm the head of state," he said.
Despite Harry and Meghan's estrangement from the royals, the couple is featured in the official souvenir program celebrating the coronation, which includes a happy photo of the family -- including Prince William, Kate Middleton and their three kids, Prince George, Princess Charlotte and Prince Louis -- celebrating King Charles' 70th birthday in 2018.
The coronation at Westminster Abbey formalized Charles' role as the head of the Church of England and marked the transfer of his title and powers. It was also the official moment he was crowned king.
King Charles was crowned with the St Edward's Crown from the 17th century, which weighs nearly five pounds, has a solid gold frame and 444 stones.
Meanwhile, his wife, Camilla Parker Bowles, was also anointed and crowned as queen. In doing so, Camilla became the first divorcee to be crowned, with the coronation invitation that was released in April making headlines when it referred to her as Queen Camilla for the first time. Until then, she was described as queen consort.
Although the actual anointment during the coronation ceremony on May 6 was not broadcast publicly, plenty of special programming and live footage from the ceremony has been airing live since 5 a.m. ET on CBS and Paramount+. Audiences will also be able to view coverage on CBS News, including the concert featuring Katy Perry and Lionel Richie on Sunday, May 7. Additionally, others can watch the coronation online on these streaming platforms.