Taylor Swift introduces surprise guests Julia Roberts, Joan Baez and Little Mix

Taylor Swift surprised her fans yet again, as two of her own heroes joined her on stage during her 1989 World Tour.

The Shake It Off singer has been enlisting her A list friends to take to the catwalk on the stage during her sell-out shows. Among those who have appeared so far are Ciara, Lena Dunham, Kendall Jenner, Gigi Hadid, Uzo Aduba, Nick Jonas, Serena Williams, Cara Delevingne and Mariska Hargitay.

But this time it was the turn of Pretty Woman Julia Roberts and legendary singer Joan Baez to take centre stage with the 25-year-old for her song Style.

The ultimate fan girls, Roberts and Baez linked arms with Swift as they strutted onto the stage wearing the singer's tour T-shirts.

Roberts, 47, took a moment to pay tribute to the legendary folk singer as she knelt down on stage before 74-year-old Joan, who handed her a red rose.

Capturing the moment Taylor shared a photo of the stars on Instagram writing: "Tonight Joan Baez and Julia Roberts danced it out to 'Style'. These two women are my heroes. What an honor." (sic)

But that wasn't the only surprise Taylor had up her sleeve. The singer was also joined by British girl band Little Mix for a rendition of their hit song Black Magic.

The pop star shared a photo of herself with Perrie Edwards, Jesy Nelson, Jade Thirlwall and Leigh-Anne Pinnock after their performance.

She tweeted: "Little Mix smashed it in front of 50,000 screaming fans tonight."

Everyone's favourite celebrity BFF Swift has previously described herself as being "obsessed" with her friends several of whom were featured in her Bad Blood music video.

The Love Story singer, who previously dated Harry Styles, is now in a serious relationship with Scottish DJ Calvin Harris.

According to a report in Hollywood Life, the Red singer is even ready to start a family with the 31-year-old DJ and the pair are believed to have been discussing baby names.

The couple went public with their relationship when Swift kissed Harris during the Billboard Music Awards 2015, held at the MGM Grand Arena in Las Vegas on 17 May.

The singer's 1989 World Tour will continue through the United States and Canada until the end of October, and she will then travel to Asia. The tour will finish up in Australia in December.

Meanwhile, Taylor is nominated for nine gongs at MTV's Video Music Awards (with seven for Bad Blood), which take place on August 30.

Watch Little Mix perform on stage with Taylor Swift: