The 18-year-old singer - who was spotted leaving a Los Angeles cinema earlier this week holding hands with the Australian pop star, who is eight years his senior - is said to be "happy" in his new relationship, but is not letting it get in the way of his music career.
When asked whether Delta is making him happy, Nick's brother Kevin explained: "I imagine so. I haven't really spoken to him much.
"Right now, he's really focused on his music. He's working with millions of other artists doing different things. It's really incredible. He has a new one in the studio every day. At 18, he's able to produce artists that have been around forever and it's so cool."
Asked whether children are on the cards for the couple, he added to In Touch magazine: "At some point for sure. Not right away, but definitely.
"That's something we always talked about early before we got married, so it's very important to us."
As they do every summer, the Martin family relocate to their summer home over the...