The actor, who plays Margaret Thatcher in the fourth season of the hit Netflix drama, caught the moment in between filming episode two.
Titled “The Balmoral Test”, the episode charts the British prime minister’s visit to the Queen’s Scottish residence alongside her husband, Denis (Stephen Boxer).
In the video, Marion Bailey – who plays the Queen Mother – can be seen leading a rendition of “Mr Sandman” by The Chordettes.
“I like it!” Queen Elizabeth II actor Olivia Colman can be heard exclaiming, clearly impressed with Bailey’s knowledge of the lyrics.
Helena Bonham Carter (Princess Margaret) and Erin Moriarty (Princess Anne) intermittently join in the singalong.
Tobias Menzies (Prince Philip) can be seen lounging in their respective chairs.
Meanwhile, Tobias Menzies (Prince Philip) can be seen lounging in his chair.
Anderson posted the clip on Instagram alongside the caption: “A royal jam.”
The Crown is available to stream on Netflix now. Find a rundown of the fourth season’s accuracy here.