Ask a Manchester City fan who their favourite players to have played for both their team and bitter rivals United down the years are and they'll reply with someone from a star-studded list.
Denis Law, Peter Schmeichel and Carlos Tevez are just some of the men who went from red for blue and in doing so, tainted their ties to Old Trafford to various degrees.
But there's one man on the scene these days that City supporters will certainly not select: Jadon Sancho.
The 21-year-old is a product of the club's academy but now plies his trade across town and went in the opposite direction of the aforementioned trio, having joined United in a long-awaited £73million transfer last summer after developing into a world-class forward over four years at Borussia Dortmund.
And on Sunday, Sancho will return to the Etihad Stadium for the first time since his hotly-deabted departure for a mouth-watering Manchester Derby in the Premier League.
But how could City - arguably the most successful English club of the last decade - let someone so special pack his bags and, eventually, move in with the neighbours?
Even Pep Guardiola doesn't know.
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"He didn't want to take this challenge, this opportunity to discover if he was able to," the bewildered ex- Barcelona boss explained in 2019, two years after Sancho rejected a contract with the Citizens in favour of signing for Dortmund.
"He decided to go there. So, it's perfect. It's going well and congratulations on what he is doing."
While Guardiola only had the England international in his ranks for his first year in charge at the Etihad - the 2016-17 season - Sancho was involved in first-team training and continued to tear it up at academy level.
Tormenting youth teams on a weekly basis, it only seemed a matter of time before the electric winger would be handed his senior appearance - but it never came.
As reported by the Evening Standard, City were confident over keeping Sancho, having offered him a club-record £30,000-a-week deal, despite his lack of first-team action.
Guardiola and director of football Txiki Begiristain saw the starlet - and Phil Foden - as central to City's future and chairman Khaldoon al Mubarak even went on record to reassure him that it was only a matter of time before he'd get a taste of proper football.
"If the end result is to get Sancho to be a starter at Manchester City, there is a balance that needs to be struck," Al Mubarak said. "There will be different paths, but the end result is how are we going to get these young men to be part of our first team."
And while local lad Foden waited patiently - soon reaping the rewards - London-born Sancho was keen to kick on, as City signed four stars who could play in his position over the course of the 16-17 - Bernardo Silva, Leroy Sane, Gabriel Jesus and Nolito - remember him?
While the following campaign marked the beginning of unprecedented success at the Etihad, Sancho snubbed the lucrative contract, leaving Begiristain to 'scold' the pondering prodigy.
He was promptly dropped from the club's pre-season tour of the United States and in retaliation, refused to turn up to training.
Guardiola, renowned for his ability to send attacking players in Sancho's mould supernova, was left frustrated - but he didn't blame his bosses.
"We tried absolutely everything to help them to play with us and he wanted to play in the first team," Guardiola declared following his £10million deadline-day transfer to Dortmund.
"There were many teams interested in him because he is a huge player, a huge talent. That is why we offered him the best contract possible to continue with us, but he decided to move on and with that we cannot fight.
"I cannot assure even the best players we have like Sergio [Aguero] and other ones, that you are going to play. I am not going to tell you 'I assure you, you will play all the games in the season' to sign the contract. I would be a liar, it's not true."
Handed the No.7 shirt by his new German club, Sancho embarked on his path to stardom in the Bundesliga and Champions League, recording a sensational 114 goals contributions in just 137 games throughout his four terms.
United couldn't ignore that kind of output and as evidenced by his willingness to join, sentiment wasn't part of the equation.
That being said, Sancho isn't salty about his previous employer.
"When I left City, there was a lot of people that doubted me – they were like 'oh you shouldn't have left Pep Guardiola' – but I just thought that it was the best thing for me," he told SoccerBible.
"I still have love for Pep, I still love everyone at the club, because they took me from Watford and helped me develop into who I am today, and obviously going to Dortmund.
"They helped with a bigger step for me – making my debut. And now I’ve made my debut I’ve expressed myself and now I’m in the position where I am today.
"I'm just so grateful to everyone who's been a part of my journey so far. Watford as well, started off life at Watford, so it's been really good."
Having spent the summer of 2020 courting him, the Red Devils opted to wait a year after BVB stood firm on their reported £117m asking price during the height of the Covid-19 pandemic.
He ultimately returned to Manchester on July 24, 2021 - for almost half the initial fee Dortmund held out for - to the delight of United fans, just weeks after City won their third Premier League title in four years.
But like with most English talents, it's claimed that Ed Woodward and co could've saved tens of millions had they acted earlier on Sancho.
Clayton Blackmore, who spent 12 years at Old Trafford at the beginning for his career, believes that his recommendation of Sancho was ignored by academy chiefs and their ignorance proved costly.
"I've been at the club at United in the academy, and I remember saying we need to get Sancho when he was 16. Nobody would stick their neck out and go 'okay'," Blackmore recalled, speaking on the ever-candid Under The Cosh podcast.
"I just watched him terrorise us in an under-16s game and then he went to Dortmund. Nobody was willing to stick their neck out and get him now. What did we pay for him now? £60m?"
The Welshman added: "It was 500k from Watford for City. But City had him in an under-16 age group with their own coach, own physio, everything they needed was for that age group, same with the under-18s and under-23s.
"I'd watched their under-18s and under-23s and he was better than any of the players in those teams and he was stuck in the under-16s. That's why he left."
But just how much does Blackmore reckon he'd have saved United?
"I'd have gone [for] 100 grand," the former Wales stalwart declared. "It's easy to say now because he's done really well."
And done well he has, establishing himself as a regular in the England squad and becoming a staple of United's attack following a slow start to life back on home shores.
Interim manager Ralf Rangnick is set to unleash him on his former employers on Sunday, with the Red Devils desperate to pull off what would be a shock result against the title-chasing Citizens.
And while United have had their fair share of ill-advised decisions blow up in their faces over recent years, what many believe to be City's most fatal could come back to haunt them.
