In the Premier League era, there have been seven players who have played for both sides - but there is one former Borussia Dortmund starlet who will no doubt be the source of frustration in pub quizzes for years to come.
That is to say that Jadon Sancho does not appear on the list of seven (well, five). While he has represented both clubs, the forward did not play for Man City at a senior level.
With that out of the way, we actually have to go back to the 2011/12 season for the most recent case of crossing 'enemy' lines.
Owen Hargreaves
The hard-hitting midfielder first moved to Manchester in 2007 from Bayern Munich to play for United.
It would be fair to describe the transfer as a relative failure, but persistent injury woes were almost certainly the sole culprit.
Hargreaves managed just 27 Premier League appearances for United before leaving the club in 2011, when he joined rivals City.
The midfielder was unable to escape his worsening knee ailments and managed just one appearance for City in the Premier League before hanging up his boots - aged 31.
Carlos Tevez
Perhaps the name most fresh in your mind, after Jadon Sancho, is the controversial former Argentina international.
Tevez was undoubtedly one of the most talented players the Premier League has seen, but he also often caused a stir or two off the pitch.
After his two-year 'lease' at United ran out in 2009, he joined rivals City in a highly publicised move. According to the Times, City paid £47m for Tevez but this was denied by the newly-rich club.
During his time in Greater Manchester, the Argentine won two Premier League titles with United, one with City, and lifted the Champions League trophy with the Red Devils.
Andy Cole
The former England striker, unlike the two names that precede him, didn't move directly from Man United to City - rather, he found himself at the City of Manchester Stadium later in his career.
Cole joined Man Utd from Newcastle in a surprise £7m deal, the most expensive in Britain at the time, where he spent eight years.
He helped the Red Devils lift five Premier League titles before joining Blackburn Rovers after falling down the pecking order at United.
In the twilight of his career, Cole joined Man City, where he found short-term success before sustaining an injury and leaving the club for Portsmouth after one season.
Peter Schmeichel
Like Cole would later do, the legendary Denmark goalkeeper spent a season with Man City in the latter stage of his lengthy career.
Schmeichel spent eight seasons at Old Trafford - one in the old First Division - picking up the Premier League trophy five times, making 292 league appearances between the sticks.
He left United in 1999 for Sporting, but returned to England in 2001 to play for Aston Villa.
After a season with the Birmingham club, Schmeichel returned to Manchester to play for City, where he made 29 league appearances.
Andrei Kanchelskis
The former Russia international was a bit of a journeyman during his playing career, but spent a good chunk of it at Old Trafford.
Kanchelskis spent five years with United, winning two Premier League titles, before signing for Everton in 1995, Fiorentina a year later and then Rangers in 1998.
During his time in Glasgow, the winger was loaned out to Man City, marking his return to England, where he made 10 league appearances before joining Aston Villa a year later.
Honourable mentions...
Terry Cooke
Now working in the US as a coach, the former midfielder is a name that often goes well under the radar.
While he did register four Premier League appearances for Man United between 1994 and 1999, beneath the shadow of David Beckham, he failed to do so with City between 1999 and 2002.
During that time the club did spend one season in the English top flight, but Cooke was loaned out to Sheffield Wednesday.
Mark Robins
A familiar story is told for the current Coventry boss, who spent his early career with Man Utd before finding himself on loan at with rivals City later on.
Robins is a product of United's youth system and managed 48 First Division appearances for his boyhood club. He left for Norwich in time for the inaugural Premier League season.
The former striker found himself in the third tier of English football in 1999, when he helped Man City to a memorable promotion.
And, of course, we've already mentioned Jadon Sancho - a current Man Utd player, who spent two years in City's youth ranks before moving to Dortmund.
