For quite a while, the question 'who is the best left back on the planet?' had a simple answer.
Obviously, it was the guy who had taken the baton from Roberto Carlos and run with it.
Marcelo had brought Real Madrid everything you'd want from a full-back: he was a steady hand defensively, he had a formidable engine, and he could attack as well and as fearlessly as any winger in world football.
In short, he was pretty damn perfect.
Displacing a guy who had made 500 appearances for the club, winning five league titles and four Champions Leagues in the process: it was always going to take some doing. Fabio Coentrao had a crack at the whip, as did Sergio Reguilon, whose world class potential would ultimately have to be realised elsewhere.
But no one really came close to succeeding until Ferland Mendy came along.
The transferal of powers was as slow as it was sure. Marcelo remained the player to beat in the weeks immediately following Mendy's arrival from Lyon, but by the end of the 2019/20 campaign, there were strong hints that they were a far more difficult side to beat with Mendy in the side.
This was a vulnerable Real team, yet they recovered to clinch La Liga, failing to lose a single one of the matches in which Mendy played from the start. That's a record that has continued to this day - when Mendy features, Real don't tend to lose.
Some might point to his fitness record as a reason to rule him out of the world class conversation, and that might once have been fair. Yet in a Real team where rotation is king under Zinedine Zidane, only Thibaut Courtois, Raphael Varane, Karim Benzema and Luka Modric have managed more minutes in 2020/21.
Only on four occasions in La Liga has Mendy failed to play for more than half an hour - three of the four have ended in defeats.
In a team littered with galactic superstars, it is never going to be Mendy who grabs the headlines, yet it's becoming more and more obvious that they cannot function without their left-sided engine motoring up and down the flank.
Improving any club in the fashion Mendy has since his arrival in Spain represents a feat of character, but it's worth remembering that this is Real Madrid. The club Jose Mourinho described, for good reason, as the club.
"He’s the Kylian Mbappe of the left-back role."- Yvan Lee Mee, Mendy’s agent
They've won 13 European Cups when second best has six. Only Juventus, across Europe's top five leagues, have won more domestic titles. Ask anyone on the street at random to name you a football club: the most common answer you will get is Real Madrid.
Playing for that club? Yeah, it's not easy.
Yet in strolls Mendy, during one of the most turbulent periods in the club's modern history, and he is completely unfazed. The pressure washes off of him like water off a duck's back. He isn't just holding his own, his mere presence is demonstrably improving the team around him. That takes something genuinely special.
Players are defined by what they win over the course of their playing career and Mendy is only just getting started in that regard. Last season's La Liga was a strong start, but Real have every intention of putting their foot on the throttle and reinstalling themselves as the dominant force in Spanish and European football.
Their best chance of doing so undeniably comes with Mendy marshalling their left wing. And that's testament to his emergence as a truly world class talent.