The TV presenting duo have a self-imposed rule that McPartlin always stands on the left and Donnelly on the right – so that they appear on screen and in pictures as Ant and Dec.
But watching their beloved football team play the Premier League match at St James' Park in Newcastle, one fellow football fan spotted that they were so focused on the game, they switched seats.
Don't let all this talk about a £300m Saudi-backed takeover distract you from the fact Ant and Dec forgot to sit the right way round pic.twitter.com/wjGRewIDPp
— Si Lloyd (@SmnLlyd5) October 17, 2021
Si Lloyd shared the photo of the Geordie due sitting the wrong way round and joked: "Don't let all this talk about a £300m Saudi-backed takeover distract you from the fact Ant and Dec forgot to sit the right way round."
It was Newcastle United's first match since Saudi Arabia's Public Investment Fund purchased the football team from Sports Direct boss Mike Ashley, after his 14-year ownership – which was not popular with fans.
"Great to be back in the Toon for an electric atmosphere. Onwards and upwards @NUFC Better days to come."
— antanddec (@antanddec) October 17, 2021
McPartlin and Donnelly previously appeared standing the wrong way round during a Sky News interview in 2017 after receiving their OBEs from the Prince of Wales at Buckingham Palace.
McPartlin said: "It's normally me first, Ant & Dec, and I'll go first, but today Dec went before me which was a break from tradition."
But Donnelly admitted: "It just looks weird, it doesn't look right!"
The pair have been friends for over 30 years after being cast as PJ & Duncan in CBBC show Byker Grove in 1989.
McPartlin revealed it was their love of Newcastle United football team that founded their friendship.
He recalled sending Donnelly a Christmas card in 1990 that said: "P.S. Fancy going to the Swindon match on Boxing Day?"
The pair have been best pals ever since and have presented a string of hit shows together including Britain’s Got Talent and Saturday Night Takeaway.
Watch: Ant and Dec react to the latest line-up for I'm A Celebrity... Get Me Out Of Here!