The One Direction heartthrob and the 'Young' singer enjoy hanging out with each other but to avoid being recognised by fans they don disguises and fake accents.
Speaking to this month's We Love Pop magazine about their recent trip to V Festival, Tulisa - who has now dyed her hair brown again - said: "We had such a good time. We were dressed in our hoodies and sunglasses, walking around the crowd. And because we're both blonde and the same height we pretended to be brother and sister!
"The second people walk past and say, 'Is that...?" we'd start being really loud, shouting at each other in northern accents like, 'What have you done with me ciggies?' or 'Pass us that bloody pint, if our mother was here now she'd blooming kill us! Aahh, come on Chez!'
"Tom and Chez are our nicknames when we get together and people look at us like, 'Oh no, that can't be them...' because we're talking in these really loud northern accents.
"Now I've given it away! We'll have to change it. Now we'll pretend to be from Liverpool."