The 28-year-old singer and the 'Game of Thrones' actress have only been together since November last year, but people close to Joe are convinced he's making the right decision in marrying the 21-year-old beauty, who's said to be mature "beyond her years".
An insider shared: "Everybody's very, very happy for them and their family and friends are all thrilled. Everyone loves them together."
The dark-haired hunk has previously dated a string of famous women, including the likes of Gigi Hadid and Demi Lovato.
But Joe is said to feel much more strongly about Sophie than any of his previous partners.
The source told PEOPLE: "She's young but is beyond her years and is crazy, crazy mature. He's never been like this with a girl.
"He was such a dater before her but their relationship was much different from the start. She was just the one for him."
She explained: "You do feel like you're living in a fishbowl. It's frustrating [that] it's the most mundane things that make the news — how boring!"
The actress also revealed she has been desperately trying to keep her relationship with the singer as private as possible.
Sophie said: "I'm in a relationship, but it's a very private relationship. I'm happier than I've been in a very long time. I very much isolated myself for a while and forgot what was fun. Going out with friends, going out to eat, not really having a care.
"And people I've met recently in my life have drawn me out of that. It really helps you own those insecurities. The things I tortured myself about before, I can forget about."