The duo posted the snap on social media, alongside the witty caption 'BeRegal'.
The app encourages users to share a photo of themselves and their surroundings in a randomly selected window every day.
Speaking to ITV News after the ceremony, Ant said the best moment was the crowning of King Charles III.
Dec added: "It was a fantastic day."
Ahead of the ceremony, they said they were "proud and privileged" to have been invited.
"It's quite surreal," Dec said, adding "to get the invite through to come to a coronation, I was like 'this has got to be a wind up', somebody has surely thought it's our time to be wound up and this is it."
They also joked they they're hoping to use the event to recruit campmates for the next series of I'm A Celebrity... Get Me Out Of Here!
Ant laughed: "There'll be a few ex-prime ministers I can think of!"
The last time the country marked a monarch's coronation was in 1953, when the late Elizabeth II was crowned Queen.
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