Pop star Harry Styles has reportedly sealed his new romance by including his rumoured girlfriend's initials in a tattoo.

The One Direction heartthrob is believed to have gone under the needle to have the initials 'Nl' inked alongside his own 'Hs'.

'Nl' reportedly stands for Nadine Leopold, a lingerie model who Styles is rumoured to have been dating since last year (14).

A source tells Britain's Daily Star newspaper, "Harry made everyone sign confidentiality agreements so the girl's letters are a secret at the moment. But he had two sets of initials together - 'Hs' is one of them of course, but everyone's saying that the other initials are 'Nl' - for Nadine Leopold."

The insider also suggests Styles ensured total privacy for the session by asking the tattoo artist to visit him at home, adding, "Harry used to go to tattoo parlours when he came to L.A. But he gets mobbed so much that he has an artist go to his house instead."