When Manchester United and Real Madrid locked horns in the last-16 of the 2013 Champions League, it was billed as “the game that the whole world wants to see”. Forget the bluster and somewhat nauseating media promotions for mundane Premier League fixtures, this fixture is box office. It may be a forbidden opinion inside the boundaries of Barcelona but this was the locking of horns of the world’s two biggest clubs.

They both possess the fan base, appeal and quality that the rest of the footballing world can only envy. That particular double header saw a number of fascinating subplots unfold: Sir Alex Ferguson dropping Wayne Rooney, José Mourinho’s apparent self-made job interview and the return to Old Trafford of the supreme Cristiano Ronaldo.

The tie itself was gripping in its entirety and ultimately the controversial decision of Turkish referee Cüneyt Çakır to send off United’s Nani proved the turning point. United and Ferguson were reduced to fury – it later transpired that this would be his final European match before retirement – and the game was arguably overshadowed by a decision that was questionable at best.

Relations between the clubs have hardly calmed in the years since. Manchester United have courted several Madrid stars including Ronaldo, Gareth Bale and most recently Sergio Ramos, who eventually signed a new long-term contract in the Spanish capital after flirting with United over a potential switch.

The bitterest episode of all happened the following month when United’s Spanish goalkeeper David De Gea’s move back to his home city broke down following a late deadline day mix-up involving fax machines. Both clubs later released statements removing themselves of blame, the frosty nature of the liaison’s evident.

But it shouldn’t have been that way. Indeed, the significance of a unique and heart-warming relationship the clubs have shared over the years has been lost amongst the drama, controversy and outrage.

On the face of it, the two represent very different ideologies. United have traditionally drawn their support from the mass working class population of Manchester and its surrounding urban sprawl. They also tend to reject nationalistic ideas – priding themselves on their Manchester roots, not their English ones. In contrast, Spain is more splintered into regions and identities than any other European state, yet Real Madrid has contemporarily maintained an identity of Spanish nationalism.

One could lazily assume that any historic associations between the clubs have been tempestuous and frosty. Sir Alex spoke in 2008 that Los Blancos were a “mob” to whom he “would not sell a virus”. In context, this was when Real Madrid were openly declaring their interest in Cristiano Ronaldo, who was developing into one of the finest footballers ever to grace the planet.

A year later United reluctantly accepted a record-breaking fee of £80 million to bring Ronaldo to Madrid, becoming the fourth United player in six seasons to make the switch – following in the footsteps of David Beckham, Ruud van Nistelrooy and Gabriel Heinze.

Relations between the clubs appeared more amiable since Mourinho arrived a year later as he continued his strong personal friendship with Sir Alex Ferguson. It’s a friendship that shares many parallels with that which existed between Sir Matt Busby and Santiago Bernabéu (main picture, left) – the legendary former Madrid striker and president whose name was given to the club’s stadium, and for whom English speakers still consistently mispronounce.

The relationship between Busby and Bernabéu is outlined in John Ludden’s book A Tale of Two Cities: Manchester and Madrid 1957-1968, where the author noted his surprise that there is some modern animosity between the clubs. “When you look back on the history and you see what Real Madrid did for United after Munich … it’s incredible.”

Busby came to Bernabéu’s attention following the 1957 European Cup semi-final, where the ‘Busby Babes’ put in a spirited performance, which ultimately wasn’t enough to stop Real Madrid, who won the tie 5-3 on aggregate on their way to retaining the trophy. Bernabéu was so impressed with the Scot’s managerial work that he offered him a job at Real. Busby was unmoved by this approach such was his desire to lift the trophy with United, and politely declined.

Manchester United’s tragedy and history changed forever the following season, when the Munich Air Disaster wiped out most of the starting line-up and rocked the club to its core. Unsurprisingly, a makeshift, young United outfit were defeated by Milan in the semi-finals, who in turn were defeated by Madrid, the eventual winners. The Madrid president, Bernabéu, dedicated the trophy to United, and even offered the trophy to the club, who refused.

Bernabéu wanted to go further, and offered Madrid’s most prized asset, the most coveted player in the world – the great Alfredo Di Stéfano (main picture, right) – to United the following year. All parties had agreed to a short-term loan deal being accepted, but astoundingly the Football Association blocked the move in the belief that it would halt the progress of a British player.

Bernabéu, and Madrid, were not perturbed in their efforts to help. They made a memorial pennant with the names of the Munich dead, called ‘Champions of Honour’, which was sold in Spain to raise money for United. They offered the use of their lavish facilities to the injured and families of the deceased for free, and then arranged a series of fundraising friendlies between the clubs

The first two of the friendlies arrived at the tail end of 1959, and Madrid won both – scoring 12 but the six they conceded showed that United were well on the way to rebuilding another fantastic side. In the fundraising banquet for the families of those rocked by Munich which followed, Bernabéu described Busby as not just the “bravest” but the “greatest” man he had ever met in football. Busby responded that “Madrid are now like our family.”

The gap on the field was closing: the following year the then five-time European champions overcame United in a classic 3-2 encounter, before Busby’s side finally beat them 3-1 in 1961 and then 2-0 the following year.

These friendlies were an incredible gesture by Madrid, helping their great rivals back on their feet following one of the greatest sporting tragedies ever. Busby’s rebuilding process oversaw triumphs in the FA Cup and then the league. Fittingly, the 1968 European Cup victory was exactly a decade on from Munich, and saw them defeat Madrid in the semi-finals before lifting the trophy. Bernabéu remarked: “If it had to be anyone, then I am glad it was them.”

These events put into perspective the animosity that has marred discussions and negotiations between the clubs in recent years. This was a world that had no commercially driven interests, no ulterior motives and no PR stunts. Bernabéu’s graciousness and generosity was admirable, but more importantly it was genuine. It was an act that should never be forgotten.

By Colin Millar. Follow @Millar_Colin