United Kingdom, March 27 -- Charlie Puth found his latest album to be the "most challenging" of his career.

The 34-year-old singer has just released his fourth studio album, Whatever's Clever!, and Charlie has opened up about the emotional process of making what he describes as his most personal record to date.

He told Variety: "What was at times most challenging for me was just how unmusical it started. We didn't start with the chords, we didn't start with sounds. We started with the topic of what we wanted to talk about."

Charlie - who performed the National Anthem at the Super Bowl earlier this year - admitted that opening up emotionally doesn't come naturally to him.

He said: "It's not the easiest thing for me to do to talk about ...