The TV presenters, who can currently be seen patting Britain's Got Talent contestants on the back every Saturday night, joined the likes of Oscar-winner Emma Thompson and pop star Katy Perry for the crowning of King Charles III and Queen Camilla at Westminster Abbey on Saturday.
Ahead of entering the ceremonial chamber, though, the pair admitted they weren't even convinced it wasn't a practical joke.
"We're very proud and privileged, I think, to be invited to a coronation. It's a wonderful day!" McPartlin told ITV News, before Donnelly chipped in with: "It's quite surreal though, isn't it?! To get the invite through to come to a coronation.
"I was like, 'This has gotta be a wind-up'. Somebody has surely thought it's our time to be wound up, and this is it. But no, it was for real and here we are. Can't quite believe it."
The pair, who are currently on-screen presenting I’m A Celebrity… South Africa, entered the abbey just before 9am in their morning suits, greeting other guests with waves and smiles.
As the pair grinned and said hello to members of the congregation in the North Transept, they were welcomed with impromptu cheers.
Best known for fronting shows including Saturday Night Takeaway, I’m A Celebrity… Get Me Out Of Here! and Britain’s Got Talent, Ant and Dec have hosted the Prince’s Trust Awards 10 times and recently collaborated with the charity on a course to make the media industry more accessible.
Australian musician Nick Cave, British Vogue’s editor-in-chief Edward Enninful, BBC director-general Tim Davie, actress Dame Joanna Lumley, TV host Jay Blades and singer Lionel Richie, who will perform at the coronation concert on Sunday, were also in attendance.
Watch: Ant and Dec, Katy Perry, Emma Thompson and Lionel Richie among celebrities invited to King Charles' coronation