Taylor Swift’s new single We Are Never Ever Getting Back Together has shot to the top of iTunes in 25 countries – and sparked intense speculation about which ex-boyfriend the song refers to.

The track – the first single off Swift’s upcoming album Red – is set to sell more than 500,000 downloads by the end of the week, according to industry sources cited by US magazine Billboard.

This would make it the biggest debut for a digital song by a female artist. Lady Gaga’s Born This Way holds the current record, hitting the 448,000 download mark in February 2011.

Since bursting onto the scene as a teenager in 2006, the country-pop princess has sold more than 17 million albums in the US and bagged six Grammys and a host of other music awards for hits like You Belong with Me, Mean and Fifteen.

She is famous for writing songs about past boyfriends, and with a list of exes that includes Taylor Lautner, Joe Jonas, Jake Gyllenhaal and John Mayer, fans are desperate to know which one the latest tune is about.

Swift’s 2010 song Dear John was taken as a swipe at folk-pop singer Mayer, and after this week’s release of We Are Never Ever Getting Back Together, Jonas was quick to deny the track was aimed at him.

“I don't think we've ever tried [to get back together] another time, so I can tell you it's not about me,” he told Washington DC radio station Fresh FM.

Earlier this week in an online chat watched by more than 72,000 fans, the 22-year-old singer discussed her new album, which is due for release in October and features a collaboration with Ed Sheeran.

Swift explained that the album's title Red reflects the power of her emotions: "Intense love, intense frustration, jealousy, confusion". She said, "In my mind all those emotions are red. There's nothing in between. There's nothing beige about any of those feelings."