Taylor Swift and Calvin Harris
Taylor Swift and Calvin Harris may walk the red carpet together of Billboard Music Awards 2015.Getty

American singer/songwriter Taylor Swift and rumoured boyfriend, Scottish singer/DJ Calvin Harris are getting serious about their relationship.

According to Hollywood Life, the 25-year-old Shake It Off singer and Rita Ora's former boyfriend may walk the red carpet together of Billboard Music Awards 2015, which will be held at the MGM Grand Arena in Las Vegas on 17 May.

"Calvin and Taylor are looking forward to attending the Billboard Music Awards as a couple," a source told the website. "It's an exciting night for them because they're both nominated for awards and can expect to win at least one between them."

"However, despite going public, it's unlikely they'll pose on the red carpet for photos together," the insider added. "Taylor doesn't mind, and has said it makes no difference now because they've taken their relationship public already, but Calvin likes to keep his personal life away from his professional life and isn't sure."

Swift and Harris were pictured shopping in Nashville, dressed similarly, both wearing grey and black.

Later, the two were spotted at a Kenny Chesney concert, getting cosy in the audience.

It was previously revealed that Swift has been single since splitting up with One Direction singer Harry Styles, after the pair dated for a whirlwind two months in 2014.

Swift has a history of dating high-profile celebrities and has previously been linked with Jake Gyllenhaal, Joe Jonas, Taylor Lautner, John Mayer, Zac Efron and Conor Kennedy.