The successful partnership between Elton John and Bernie Taupin always worked on the same principles – until the day when the performer forced his co-writer to break the rules that made them both famous.

For one, they never wrote songs with the intention of creating hits; they had stories to tell, even if the reserved, introspective Taupin presented himself very differently from the outlandish party animal John. For another, whether it was Taupin pursuing a lyric idea or John chasing a melody, they would abandon any concept that didn’t start working for them in a matter of minutes. For another, with the exception of suggesting a title from time to time, John didn’t tell Taupin what to do.

All three of those hard-and-fast rules went sideways after John decided he wanted to write a song for his friend, tennis champion Billie Jean King. “In the summer of 1974, we were driving to one of his concerts and he looked over at me in the back of the car (I can remember, he was on my right) and he said, ‘I want to write a song for you,'” she recalled in an interview on John’s website. “I turned scarlet red, I’m sure, and went, ‘Oh, please. What?’ And he goes, ‘No, I want to write a song. What are we gonna call it?’ And I said, ‘I don’t know!’ Then he went, ‘How about “Philadelphia Freedom”?’ Because I played for the Philadelphia Freedoms [tennis team], and he used to come to watch our matches.”

John decided early on that he was aiming to write a hit, in contravention of the writing team’s standard procedure. “At the time, we were making so many albums, but we liked to make separate singles too," he explained in 1990. "I said to Bernie, ‘Will you write a song called "Philadelphia Freedom" for me? Thank you, Elton.’”

“Not exactly the easiest title to deal with, I might add," Taupin noted.

Listen to Elton John's ‘Philadelphia Freedom’

It was a steep challenge for other reasons too. "I have to be very conscious of the words I put in his mouth,” Taupin told The Telegraph in 2002. “I still write what I feel, but when I've finished a song, I have to see if it's something I want to present to him or if it's more suited for use elsewhere.” In the end, deciding that he couldn’t write lyrics about tennis, Taupin gathered some feel-good lines and sent them to his longtime co-writer, who indulged his passion for Philly soul to complete a song that hit No.1 in April 1975.

A few months later, the notoriously moody John, at least temporarily, regretted the exercise, telling a paper, “In America I’ve got ‘Philadelphia Freedom’ going up the charts again. I wish the bloody thing would piss off. I can see why people get sick and tired of me. In America I get sick and tired of hearing myself on AM radio. It’s embarrassing.”

What was done was done – and in any case, King was delighted with the song, which went on to become an unofficial anthem for a wide range of sporting endeavors. “It’s a feeling,” she said in 2017. “It’s a great song for a team. It’s a great song if you’re not a team. The people in Philadelphia go, ‘That’s our anthem.’ And half the time they don’t know the backstory.”

As the years rolled by, John and Taupin have come to spend less and less time together, though their partnership has weathered worse storms than the one over “Philadelphia Freedom.”

Speaking in 2002, Taupin noted, “The only thing we really have in common is the music and talking about it. When we talk on the phone, he goes, ‘Hello, what's going on,' and I tell him about my latest horse. … I can feel his eyes glazing over at the other end. He will tell me about his parties and so on, and I am not really interested either. And then we talk about the new so-and-so record we are listening to, and we’re back where we were in 1968. The music has been the catalyst for everything we've ever done.”