The collaborative project with Netflix saw Duke visit UK landmarks such as the Royal Naval College in Greenwich - which provided the backdrop to several key scenes in season three.
Meanwhile, St Mark's Church in Berkshire - which just so happened to be where Pippa Middleton wed James Matthews in 2017 - was used to shoot the royal family's Sunday worship ritual.
"Following in the footsteps of such golden splendour was quite an extravagant feeling - standing where Olivia Colman, Her Majesty, spoke her speeches as she firmly commanded a country," he captioned the post.
"This series is woven through the history of Britain, filmed all over the authentic landscape and architecture of the United Kingdom, and done so with the utmost respect, honour, and justice to The Crown."
"Every member of the cast embodies their true-to-life persona with talent and suave, it's truly a delight to watch this series grow into the arms of the nation," he continued. "Season four is already gearing up to be an intense insight into the next chapter of the royal family."
Duke has been working on the Instagram account for two years and it's a must-follow for serious cinephiles with references to films and television shows including Friends, Bohemian Rhapsody, Downton Abbey and The Girl On The Train.
Those inspired by the account will be pleased to learn that a number of the filming locations used for season three of The Crown are open to the public - unlike the Queen's private Buckingham Palace quarters.
Winchester Cathedral in Hampshire, England was hired to recreate former prime minister Winston Churchill's funeral in 1965 which famously took place at St Paul's Cathedral in London.
While Hylands House in Essex, England was made to look like the White House for the second episode of season three which sees Princess Margaret and then-husband Lord Snowdon visit the US in a bid to strengthen Anglo-American relations at the request of Her Majesty.
Anyone else already planning a trip to Old Blighty?