Despite the two big Manchester clubs reaching the FA Cup final for a combined 31 times, this afternoon at Wembley will be the first time United and City have actually met in the final.
While City are strong favourites, there is no question United would love to upset their bid for the treble and you can be sure it will be a fiercely fought encounter.
United have won the FA Cup 12 times and this must be the first time they have gone into a Wembley final as heavy underdogs.
But before we get stuck into today's action, it is an appropriate time to recall this is the 100th anniversary of the first-ever Cup final at Wembley in 1923 which will always be remembered for its chaotic scenes and a white horse.
An estimated 250,000 fans showed up at the ground, which at that time had a capacity of 127,000.
Wembley was already at full capacity two hours before the 3pm kick-off and thousands continued to pour into the ground.
The spectators had little alternative but to spill over onto the pitch and the Times reported "the pitch became a sea of people".
King George V arrived 15 minutes before the scheduled kick-off and amazingly, amidst all the chaos, everyone stood at attention for the national anthem.
Fortunately the crowd was well behaved considering the circumstances and the game between Bolton Wanderers and West Ham United was able to kick off only 45 minutes late, with thousands of fans on the touchline.
Several times the ball remained in play after bouncing off spectators lining the pitch. It was an incredible sight.
Bolton went on to beat the Hammers 2-0 but the result was all but forgotten because of the extraordinary scenes.
It became known as the "White Horse Final" because the press portrayed policeman George Scorey on a white horse called Billy as singlehandedly saving the day as the mounted police cleared crowds from the pitch.
There were other policeman on horseback all doing their bit, but Billy was the only white horse and received the overwhelming media attention, the horse standing out in all the photographs.
Scorey, who despite his name had no interest in football, took it all in his stride.
He admitted afterwards that he initially thought his task was "hopeless" but he was inspired by the horse.
He told reporters: "I didn't know where to start… but Billy knew what to do. He pushed forward quietly but firmly and the crowd made way for him.
"He answered all my orders beautifully. The crowd seemed to respect the horse."
When Scorey returned home that night and his girlfriend asked him what sort of day he had, he replied: "Just ordinary lass, just ordinary."
It will be anything but ordinary at Wembley this afternoon and many believe this will be a tougher match for City than next week's Champions League final against Inter Milan.
Hopefully there won't be any need for horses on the pitch.
City manager Pep Guardiola will have one eye on the Champions League which may affect his selection.
However he has such a wealth of players to choose from it doesn't really matter.
Whoever is in his starting XI, Guardiola will still have a host of international stars on the bench.
United boss Erik ten Hag doesn't have quite the same luxury of choice at his disposal.
The hamstring injury to Anthony Martial will not have helped as he needs firepower up front to support Marcus Rashford.
FA Cup finals are often disappointing. Let's hope this one isn't.