The 'Promises' hitmaker only released their latest record, 'Love Goes', in October, but Sam is already hard at work on the follow-up.
His longtime songwriting partner, Jimmy Napes, told the 'Straight Up' podcast: “We wrote a song just the other day and it’s one of my favourite things we’ve ever done. Continuing to just do this and it still feels like the first time, essentially, that’s a really special partnership."
Gushing over the 'Too Good at Goodbyes' singer's breathtaking vocals, the record producer continued: “Sam’s voice is obviously one of the greatest voices I’ve ever heard.
“To be able to have that voice expressing the music that you’re writing together, it’s like a joke.
“It can be a little bit of a trick because Sam could sing the phone book and it would sound amazing.”
Jimmy also admitted that the pair have penned a lot of tunes over the years that have ended up being "binned" by Sam's record label.
He added: “On the whole a lot of the songs get binned.
“We, even on the day, might be jumping up and down saying. ‘I love this’, and then people in the team will just be like, ‘This is the worst thing I’ve ever heard’.”
Meanwhile, heartache has been a prevalent theme in Sam's music, but the end of their first serious relationship with '13 Reasons Why' actor Brandon Flynn in 2018, was the first time they'd felt "real" heartbreak.
The Grammy-winner said of 'Love Goes': "I'd say [this was] the first proper time I've been actually heartbroken. That feeling of they're gone, you can't sleep, the really, really bad feeling.
"The others were the idea of it and it was pure unrequited love. This, I would like to say that we loved each other. So, I definitely, definitely loved him. So yeah, it was proper.”
