The boyband heartthrob was appearing on US entertainment show Extra when the host asked the group to shout out their celebrity crush with no thinking.
Nathan got plenty of cheers from the crowd when he chose American actress/singer Ariana, who he began dating earlier this year after they met while working on the song 'Almost Is Never Enough'.
The couple have quickly become one of the cutest celeb pairs around and were recently able to spend time together when Ariana jetted into the UK to promote her first album Yours Truly, which has already been number one in the US.
According to The Guardian, when their reporter turned up to interview her she was sitting on Nathan's lap. Clearly they can't bear to be apart! But when the reporter quizzed Nathan on being in a high profile relationship he simply replied: "It's not my interview." Aww. Letting his lady take the limelight. Very romantic.
While plenty of couples would find being apart for long periods of time difficult to cope with, Ariana recently said that it doesn't matter to her and Nathan because they are so happy.
"We have the same management so it's easy to look at each other's schedules and pick out a certain time. But we're not separated for more than a week at a time, usually," she told The Sun.
"It doesn't even matter. It's just such a happy thing. The distance doesn't really take a toll when you're that happy."
Watch Nathan and Ariana's duet 'Almost Is Never Enough' below: