In 2014, there weren't many people who felt Kurt Zouma was going to be anything other than a future star.
The 19-year-old centre-back joined Chelsea for a fee of around £12m, and by late 2015, he was a regular starter at Stamford Bridge alongside John Terry, looking exactly like the long-term replacement to the Englishman that most felt he could be.
His world came crashing down in February 2016 when he ruptured his ACL in a meeting with Manchester United, and after a year of recovery, he was tasked with working his way back to full strength.
A loan with strugglers Stoke City was his first test, and after he proved his athleticism was back, he was sent out to Everton to showcase his defensive ability, and after one unconvincing season back at the Bridge, Zouma is now making up for lost time.
The 26-year-old is back to his athletic peak, dominating defenders both in the air and on the ground, but perhaps the biggest improvement we have seen from Zouma is in his head. A large part of last season was spent making foolish mistakes, but those appear to have been largely eradicated.
Many are quick to credit his resurgence to Thiago Silva, his 36-year-old new partner at the heart of Chelsea's defence, and there's some logic to that. Against both Sevilla and Manchester United, the Brazilian's calming influence was clear as he encouraged Zouma to think about things before lunging a leg at the ball.
However, to take all praise away from Zouma is unfair. Let's not forget, he was clearly Chelsea's top defender after lockdown (admittedly not the most impressive honour of 2020), and all the signs were there that he was ready to get back to his best.
Zouma brought his desire and physicality to the new season, where he has been met with Silva's cool head, and the pair have combined to create probably the league's top centre-back duo so far this season.
He may have had a four-and-a-half year delay, but Zouma is now the player Chelsea always expected him to be - a top-class defender capable of leading the line for years to come.
At the minute, Zouma is clearly relishing a 'lack of responsibility'. He's not Chelsea's leader. He's not the man tasked with organising and structuring those around him. Those responsibilities have gone to Silva, allowing Zouma to focus purely on his game.
Communicating with each other in French, Silva has been telling Zouma what to do, and the 26-year-old has been doing it. He's almost acting as Silva's legs, and it's a relationship which has brought some fantastic rewards so far this season.
It's the kind of bond we should have been seeing between Terry and Zouma until the former's departure in 2017. Most young players need that kind of mentoring, but for Zouma, it's come as a 26th birthday present.
The ideal outcome from this would be Silva passing his leadership on to Zouma, who could assume responsibility once the Brazilian inevitably walks away from Stamford Bridge, but even if that doesn't happen, Zouma will still be a far better defender thanks to the experience he's gained this season.
It's for this reason that Silva likely has to be viewed as Chelsea's signing of the season if this continues. Sure, he doesn't make the saves of Edoaurd Mendy or contribute to goals and assists like Timo Werner and Hakim Ziyech, but the lasting impact he has on those around him is invaluable.
For Zouma, Silva's arrival came at the perfect time. His doubters were almost so vocal that a move away from the Bridge was quietly mooted, but he has put his head down, worked closely with those who know better than him, and he's shining.