"The Land Rover was made in 1966 and is a Series 2A with some modifications. It was used by The Duke of Edinburgh for many years," the caption read.
Philip, who died on April 9 at the age of 99, was a big fan of Land Rovers, so much so that at his funeral, his coffin was carried on one that he that designed.
The Land Rover was "designed and custom-made to the duke's specification," Buckingham Palace said.
William and Kate also took to Instagram to share footage of their movie night, where they took the time to go around the cars and speak to those who attended.
"Movie night at the Palace of Holyroodhouse for NHS Staff..." Kate wrote in the caption.
"As Joint Patrons of @NHSCharitiesTogether, William and I are absolutely delighted that so many of you could join us here tonight," the Duchess added.
The pair hosted the night in recognition of healthcare workers' vital work throughout the pandemic, and described it as a night of "escapism".
"We wanted to thank you for the extraordinary dedication, commitment and personal sacrifice you have shown in supporting our communities through this pandemic.
We invite you to grab your popcorn, cuddle up under your blankets and be transported to 1970s Britain for an evening of much-deserved fun, drama, glamour and escapism!"