The Irish singer began dating 20-year-old aspiring model and actress Amy Green after they met in a London nightclub back in October (12).
However, Horan has now called time on their romance because he is too busy with his pop career to be in a relationship.
A source tells Britain's Sunday Mirror, "Sadly, it is over between Niall and Amy. He finished it because he didn't have enough time with everything he has to do.
"Understandably she was disappointed because she had been in a relationship before she started seeing Niall and chose him over her boyfriend. But there are no real hard feelings and they're still close."