MANCHESTER, England -- John Stones has been so good during Manchester City's charge toward the treble that during a party to celebrate winning the Premier League title, Kyle Walker grabbed the microphone and began singing the song dedicated to the England centre-back by the club's fans.

Walker belted out "Johnny, Johnny Stones" to the tune of Boney M's "Daddy Cool" in front of a packed dance floor at Manchester restaurant MNKY HSE before the rest of the crowd joined in.

Stones, thriving in a half-defender, half-midfielder role dreamt up by manager Pep Guardiola, has never been more popular. Along with 52-goal striker Erling Haaland and midfield genius Kevin De Bruyne, he will be one of the first names on the team sheet when Guardiola names his XI for the Champions League final against Inter Milan in Istanbul on Saturday. But it hasn't always been that way.

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Three years ago, in the summer of 2020, it looked like Stones might have to leave the Etihad Stadium. Struggling with fitness and form, he could barely get a game.

"It was probably one of the hardest times in my career," he tells ESPN. "I literally went back to firstly looking at myself, being super critical of myself and what I could do better on the football pitch, and then looking into every fine detail. Food, what food? Training, what training? What extras?

"I would go home and do work, even late at night, or straight after training. These small margins, put them all together to kind of break where I was at. It was a big learning curve for me."

The low point was the Champions League quarterfinal against Lyon -- delayed because of COVID-19 -- in August 2020. Stones was fit and Guardiola used a system incorporating three central defenders but instead picked 35-year-old Fernandinho and 19-year-old Eric Garcia. City crashed out after a shock 3-1 defeat in Lisbon and Stones was an unused substitute.

"I think it's not just that game," he says. "I think any game that you don't play, or feel maybe that you should be playing, every player feels like that when they don't play, especially here because we've got an incredible team, it's always difficult. I really do try to put a positive spin on that and use that to motivate me."

In the wake of the defeat to Lyon, Stones was linked with a return to Everton, the club he left to join City in a £47.5 million deal in 2016. Ruben Dias arrived from Benfica in a move worth more than £60m to further complicate his path into the first XI and, because of a chequered injury record, there were doubts about whether Guardiola and director of football Txiki Begiristain wanted to extend his contract.

Stones, though, insists that a move elsewhere was never on his mind.

"I never thought about that," he says. "I think as soon as you accept that or have that mindset then you have killed yourself. So no, I always wanted to stay; I have stayed and I absolutely love it. I wanted to prove to myself, I didn't say to anyone, 'It was because I want to prove to you.' I think, if anything, you have to prove to yourself first and foremost that you deserve to be here, you are good enough to be here, and what you bring to the team."

It's a decision that has paid off. Less than a year after warming the bench against Lyon, Stones was named in the PFA Team of the Year alongside Dias as City won another Premier League title. A few months later, he signed a new five-year contract that will keep him at the Etihad Stadium until at least 2026.

During the second half of this season, he played in a hybrid position that has required him to step out of defence and into midfield and then back again. He was so impressive in Saturday's FA Cup final against Manchester United that Jack Grealish labelled his performance "disgusting" in a postmatch interview. More than once, the blue half of Wembley sang "Johnny, Johnny Stones."

"People have always said from a young age that they can see me playing in midfield," he says. "I think I did, and still do, love playing as a centre-half and I've absolutely loved this role as well. I think I have shown myself that I'm able to do it. Maybe showing some attributes that I didn't know that I had, but the manager has seen [something] in me and ultimately I think I'm just trying to show what I can do in there, and show what the manager sees in me."

Stones will be asked to do it again Saturday at Istanbul's Ataturk Olympic Stadium when City take on Inter for a chance to win the Champions League for the first time and complete the treble. Guardiola's team are heavy favourites, but Stones has learned over the course of his career that nothing in football is guaranteed.

"Inter are in the Champions League final for a reason," he says. "They've got incredible players, we can all see that. How they played on a big occasion, in a derby game [against AC Milan] in the Champions League semifinal, is never easy. We know what we're up against, they are an incredible team, and I know I am going over and over but we have to be ourselves and focus on us."

Stones is trying not to look too far ahead but there is an acceptance, if only briefly, that lifting the trophy would represent quite the turnaround after the lows of 2020.

"Probably, yeah," he says with a smile. "For me personally, if I hopefully look back after Saturday, with a winner's medal. Yeah, it will be super sweet."