The venue is where Harry, younger son of heir-to-the-throne Prince Charles, Wednesday USA actress Meghan Markle at a glittering ceremony in May and Eugenie is copying some of her cousin's plans for her big day.
Prince George and Princess Charlotte will be among the pageboys and bridesmaids at the wedding of Princess Eugenie, Buckingham Palace has said.
Just one day before Princess Eugenie and Jack Brooksbank say "I Do" at St. George's Chapel, royal watchers are getting a better sense of what to expect at the ceremony. And just like Harry and Megs, the couple have also invited members of the public - 1,200, to be exact - to witness the big day up close and personal.
Also spotted outside Windsor Castle was a floral delivery featuring pink roses, though the overall floral theme for the wedding remains under wraps.
The bride's sister, Princess Beatrice, 30, has been confirmed as the maid of honour, while Jack's brother Thomas Brooksbank will act as best man.
Princess Eugenie interjects, saying, "Yes, and I thought, 'What a silly hat!'. and I thought, 'Who's that?' and then you came over and shook my hand and I was all butterflies and nervous".
The couple get married on Friday in Windsor, Berkshire.
The This Morning at the Royal Wedding show continues until 12.30pm. It was not certain whether the 92-year-old queen's husband Prince Philip, 97, who no longer carries out official duties, would be present.
And with the presence of so many royals - and a number of celebrity guests - extra security measures have been put in place.
Jack describes Eugenie as "incredible", praising her multi-tasking skills and confirming she was far from a "bridezilla" in the planning process. It has criticized the royals for using weddings as "PR exercises" and expecting taxpayers to pick up part of the tab.
These concerns aren't popular in Windsor's business community, where the surging popularity of the royal family in recent years - and the afterglow of Harry and Meghan's wedding - has helped bring in visitors in recent months.