The One Direction hunk, who has been dating the Hungarian model since December last year, is single again after the pair found it difficult to make their relationship work due to their hectic work schedules.
A source told The Sun newspaper: "There was no big fall out, things just fizzled out as Niall and Barbara are both working in different parts of the world.
"They are both really busy and Niall is focused on recovering and getting ready for the band's massive Where We Are tour.
The insider added that they are "still in touch and friendly" and simply found it hard to see each other while Niall, 20, was in Britain recovering from major knee surgery and Barbara, also 20, continued to travel the globe with her work as a Victoria's Secret model and L'Oreal ambassador.
The stunning brunette, who is based in Paris, confirmed she had split from Niall by posting a romantic photograph of herself and a new secret guy on her Instagram account, clutching a bunch of flowers. It was accompanied by the caption, "Early Valentine".
Barbara and Niall have been spotted together on a number of occasions since they started dating, including backstage at 'The X Factor' and at a JLS farewell gig at London's O2 Arena, where they band waved goodbye after five years.
The couple were also seen enjoying a cosy dates in Hertfordshire, playing golf and visiting a local pub and celebrated New Year together at Westminster Central Hall in London, where Gary Barlow hosted a special concert.
Irish Niall and his band mates - Harry Styles, Zayn Malik, Liam Payne and Louis Tomlinson - are on a three-month break after touring the world and Niall is having intense physiotherapy ahead of rehearsals before the group start touring again.
Meanwhile, Barbara is also trying her hand at acting and recently secured a role in 'Hercules: The Thracian Wars', which hits screens later this year.