The duo, both 20, huddled under an oversized black umbrella as they arrived at BBC Radio 1 studios on Friday afternoon (11 October).
Despite the chilly weather in the capital (and rain), Ariana flaunted her tanned legs in a teeny tiny red check mini skirt and skyscraper monochrome heels. She did, however, keep toasty warm on top, choosing a fluffy white cardigan.
Nathan, meanwhile, went for a casual all-black look and trainers as he accompanied his girlfriend on a day of publicity for her new TV show Sam & Cat and her new album, Yours Truly.
The Wanted heartthrob confirmed his relationship with US singer/actress Ariana last month, following the release of their duet 'Almost Is Never Enough'.
After photos of them holding hands emerged, he tweeted: "So, I guess it's obvious now … Thanks to everyone who is being so lovely. I'm so happy #butweareterrified #pleasedontkillme #orariana."
Victorious star Ariana then added: "We hesitated saying anything as people can be a bit insensitive but thank you, we value all of your happiness, thank you for valuing ours."
The teenager has been in the UK with Nathan this week and appears to be enjoying England. Today she tweeted that it was a rainy day in the capital along with a heart emoticon. Believe us, Ariana, it can get old fast! She also shared a picture of a cup of tea along with a heart symbol.
Her new show Sam & Cat is a spinoff of Nickelodeon series iCarly and Victorious.
Watch Nathan and Ariana's 'Almost Is Never Enough' video below: