The X Factor star wore ripped jeans with black ankle boots, a cat print jumper and a leather jacket draped over her shoulders, to create a rock-chick inspired ensemble.
Diana, who is dating long-term boyfriend George Craig, has become one-to-watch in the style stakes, so perhaps it's no surprise she was seen rubbing shoulders with fashion industry experts.
The young star brightened up her outfit with a pink Kate Spade New York designer handbag.
After designing her 'Dee V' range for Very in 2011, Diana told Reveal last September that she'd love to pursue more fashion work.
"I'd love to get into fashion," she told us. "I already worked with Very, which was cool. If the right thing came up at the right time, I'd definitely get stuck in!"
Diana rose to fame after starring on The X Factor in 2008 and went on to release two albums, Songs from the Tainted Cherry Tree in 2010 and follow-up album, Music to Make Boys Cry in 2013. Diana will also star in new Sky comedy show, Give Out Girls, which is expected to air later this year.
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Watch Diana's music video for 'Music To Make Boys Cry' below: