Sweet Nemi shock! One Direction's Niall Horan calls Demi Lovato ‘honey' in birthday message on Twitter

Niall Horan has sent One Direction fans into a Twitter frenzy after sending a birthday Tweet to Demi Lovato openly calling her ‘honey'.

The pair have been friends for some time and, despite rumours that they've been secretly dating, they've always denied a romance.

Yet Niall's message to the US X Factor judge couldn't have been more affectionate.

‘@ddlovato happy birthday honey!' Tweeted Niall, 18.

‘Have a lovely day! See ya soon'

Demi, 20, responded, ‘@NiallOfficial thank you sweet stuff! :)'

The loving exchange caused so much excitement on Twitter that the term ‘Nemi' was soon trending.

But Niall, who spent the weekend partying at V Festival, is too exhausted to say more.

‘Soooo tired today!' the 1D lad told his Twitter followers.

‘Big weekend!'