Let's put this into perspective: at the end of the 1994-95 season, Gillingham Football Club were beset with financial problems, and were teetering perilously on the brink of extinction.
At the time, die-hard Gillingham fans would leave Priestfield stadium after another dismal performance and would be met with something worse than seeing their side lose: people outside the ground advertising their superior rivals, Charlton Athletic, telling them to forget about the local club they've supported for decades and watch their rivals instead.
Whilst Gillingham were languishing in the lower depths of the Football League, Charlton had been rising high in the English Premier League mixing it up with the likes of Manchester United, Arsenal, Chelsea, and Liverpool.
But despite their success in the higher echelons of English football, the southeast London club have long been accused of tapping into the Kent (a county in the southeast of England) market and stealing fans from Gillingham's main target area.
Bear in mind, this is a football club who have long been theoretically superior to Gillingham, playing in a higher league for almost 90 years.
As the understandably angry Gills' chairman Paul Scally put it, "Charlton [Athletic] are in SE7 (officially an area of London), not Kent. They're no more a Kent club than Crystal Palace or Millwall (east London clubs who have no official affiliation with Kent). Why can't they get enough people to fill their stadium from the Charlton area?"
So for many years in the past decades and recent times, while Charlton have achieved gate receipts of over 26,000 spectators regularly, the Gills have had to make do with numbers of around 5,000-6,000 per game for a stadium that holds almost 11,000.
Therefore, there are many reasons as to why Gillingham can dislike Charlton Athletic, a club who could be said to have broken codes of etiquette and unfairly hindered the development of the Gills, Kent's sole representative in the English professional football hierarchy.
And now, for the first time in almost a century, both these clubs are on equal footing and participating in the same league, the Coca-Cola League One.
So what better way for Gillingham to exact revenge on their increasingly bitter rivals than to beat them at their rivals' own fortress, a place where Charlton have deviously tried to lure loyal Gills fans.
Then again, what better way is there for Charlton to maintain their superiority complex over Gillingham by completely crushing them on their own ground?
With an away following of close to 4,000 for this match at The Valley on Saturday, this could well be considered Gillingham's biggest game of the season.
They are fighting relegation and continue to be dogged with financial limitations, so a positive result away to Charlton will almost certainly give the Gills that vital morale boost required to aid their League One survival battle.
For Charlton, a win against fierce rivals Gillingham will also give them a big confidence boost, something that could be vital in their fight for League One promotion as they currently are five points off the automatic promotion places.
For both clubs, a win on Saturday will not only dramatically boost morale, ease their league table concerns, and give them the bragging rights, but it can also potentially be the pivotal point in the two clubs going forward as a footballing franchise.
This is especially the case for Gillingham, a club who perhaps need the financial security of regular League One football in order to avoid a deleterious repetition of the infamous '94-95 meltdown season.
So whilst Manchester United taking on Liverpool at Old Trafford is big news, and could possibly decide who wins the Premier League and who gets into the UEFA Champions League next season, there is a more decisive match going on.
Charlton Athletic against Gillingham at The Valley isn't just about attaining the three points needed to get promotion or avoid relegation.
It's not about winning another league title or getting into a major competition yet again.
For Gillingham, it's about gaining revenge for years of preventing the growth of their football club.
For Charlton, it's about ensuring the superiority complex remains intact, and proving who really is the better club with the bigger fan base.
Most importantly, it's about Gillingham showing the solidarity of their football club, and proving that fans will love their team even through the most adverse conditions.
It's Charlton Athletic Football Club versus Gillingham Football Club, and it's probably the most important match happening this weekend in English football.