Fifth Harmony can't believe the success of their single Worth It.

The American girl group have become a worldwide hit since forming on the US version of The X Factor in 2012.

But they only recently achieved their biggest hit to date, after Worth It became the girls' first track to sell over one million downloads.

Now they are on a par with hit artists such as Taylor Swift, and are struggling to come to terms with their new level of fame.

"This is definitely our biggest single to date for sure, and so just to see it continue to climb and see it on the charts with Ed Sheeran or Taylor Swift, or whoever's big right now, it's right next to them and right there with them," singer Lauren Jauregui told Billboard magazine. "It's frickin' platinum! To say it's platinum, that a million people bought that song, it's amazing. It's so incredible to see that the support has gone beyond our fan base."

The group previously released singles such as BO$$ and Sledgehammer, which were both well received by fans.

But they admit they had no idea that their latest offering would be such a hit.

"With Worth It, we were really surprised," Normani Kordei added. "We love the song, but we were kind of surprised, to be honest."

"It's normally the songs that you don't really think that are the hits!" Dinah Jane Hansen agreed.

Fifth Harmony previously revealed they have stuck together and avoided falling victim to the girl group curse.
Instead of arguments and cattiness, the five-piece band have become close friends.

"We've been through the highest points of our lives together and the lowest points of our lives together. Through that process you get to know the best of people and the worst of them, and I feel like respect is knowing both and being able to surpass the negative things," Lauren told