Those who can marry there include knights, residents of Windsor Castle, residents of St. George University, and of course members of the royal family.
If you fall into any of these categories, you will need to obtain permission from the Queen herself.
This means that even Mrs. Gabriella Windsor, Prince Harry, and Princess Beatrice (all relatives of the Queen) had to seek permission.
A statement from Kensington Palace regarding the Sussex couple’s wedding said:
“The royal family bears the cost of the wedding.”
Can I get married at Windsor Castle? UK | News
Source Can I get married at Windsor Castle? UK | News