The 28-year-old singer-songwriter has previously collaborated with Frank and has admitted to learning a lot from working with the American star - but he doesn't claim to understand all of Frank's character quirks.
He shared: ''He's such an idiosyncratic. He's so instantly recognisable. It's not just his voice it's turn of phrase. That's just something remarkable that I have learned a lot from.''
And asked how they connect on an emotional level, James said: ''We're quite different in a lot of ways. But the songs that I've had input to on his record, I don't really know in what part of the middle we met.
''He's an anomaly, it's quite hard to describe that relationship, so I'm not gonna try. ''
James has also recently collaborated with rap star Kendrick Lamar on his track 'ELEMENT' and he explained how their partnership came about.
He told The FADER magazine: ''We'd been in touch various times and he'd come to the studio and listen to stuff and we got on and I sent him some music while I was on the road when I was in Mexico. I got an email and he said, 'Can you turn something in tonight?'
''I sent him a thing that I'd done and he took the chords and that became a part of 'ELEMENT'.
''I think that that was not the most organic way, sending music to someone by internet and it ends up in a tune, but I just knew that I could trust them with my music because they have a flawless record of production, that unit that Kendrick works with.''
Take a look back at October's inaugural event.
The film is expected to continue without Mendes' involvement.