The Irish singer was first linked to the Victoria Secret's beauty last year (13) and they were pictured together on a number of dates.
However, a new report suggests the couple recently parted ways after struggling to maintain a long-distance relationship.
A source tells Britain's 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."
Palvin hinted at the split this week (beg10Feb14) when she posted a picture on Instagram.com which shows her clutching a red rose and posing with a mystery man, alongside the caption, "Early Valentine! Paris."