The prince will be sitting between Princess Eugenie’s husband Jack Brooksbank and Princess Alexandra - the cousin of Queen Elizabeth whose last royal working engagement was a decade ago.
Also in the third row will be Prince Andrew’s daughters Eugenie and sister Beatrice, with her husband Edo Mapelli Mozzi.
Front-row seat allocations are reserved for senior working royals, which include Prince William and Kate, Edward and Sophie, their children Lady Louise and James, Earl of Wessex and Princess Anne and her husband Tim Lawrence.
A close source told The Sun: “There were discussions that the seating could be arranged on line of succession.
“But that would have put fifth-in-line Harry front and centre — and with William and Kate.
As they chatted and took selfies with fans, the Princess of Wales shared: “Yeah, we’re all good. Hopefully a bit like swans — relatively calm on the outside, but paddling on the inside.”
Cheerful Kate spoke of her children George, 9, Charlotte, 8, and Louis, 5: “They are really well, thank you. Excited, a bit nervous obviously with the big day ahead. They can’t wait.”
When asked how King Charles was feeling before his crowning, she said: “Looking forward to it as well.”
She added: “It’s nice to be out here and saying hello to everyone who has obviously stayed out here for so long. And obviously will be staying out here overnight.
“It’s going to be long. Are you tired? It is long hours for everybody, isn’t it? It’s a really great moment. A celebration as well. We have an early start but I think everyone has.”
Charles, Kate and William shook hands and shared their appreciation with patriotic fans along The Mall.