Their friendship is so strong that Charlie was an usher at the Duke of Sussex's wedding to Meghan Markle, and Harry was then Charlie's best man at his August 2018 wedding to Daisy Jenks.
The wedding, which was just months after the Sussexes' own nuptials, was also attended by Duchess Meghan, and Princess Eugenie and Jack Brooksbank.
While Charlie and Harry are close friends, Charlie's brother Thomas van Straubenzee is also a good pal of Prince William.
Thomas is one of Princess Charlotte's godparents - so it sounds like Archie is in good company.
Before the big day, Buckingham Palace released a statement regarding the ceremony.
"Archie Harrison Mountbatten-Windsor will be christened in a small private ceremony by the Archbishop of Canterbury in the Private Chapel at Windsor Castle on Saturday 6th July.
"The Duke and Duchess of Sussex look forward to sharing some images taken on the day by photographer Chris Allerton.
And when it came to the godparents, the couple were adamant they should be kept a secret.
"The godparents, in keeping with their wishes, will remain private,” the statement said.
Things haven't gone exactly to plan, with Charlie being named as Archie's godfather, however it remains to be seen whether the identities of the royal baby's other godparents will be released.
