Taylor Swift got the London-leg of her Eras tour off to a good start, with the UK's Prince William posting a backstage picture of them posted on social media Saturday.

After celebrating his 42nd birthday at Swift's Wembley Stadium concert with his children, Prince George and Princess Charlotte, William posted their backstage selfie.

The US pop sensation seemed equally enamoured, posting a photo with the three royals and her boyfriend Travis Kelce.

"Happy Bday M8! London shows are off to a splendid start," she wrote on X, formerly Twitter.

A widely shared video on social media appeared to show William, who is the heir to the throne, dancing energetically to Swift's hit single "Shake it off".

Also among the nearly 90,000 fans packed into the stadium was Labour party leader Keir Starmer, who with his wife.

Starmer, who after next month's election could be Britain's next prime minister, said on Saturday that Swift "was fantastic. Absolutely fantastic".

"I know I will be asked what is my favourite song and I am not going to pretend I have got every album and know every song," he told reporters on the campaign trail. 

"Although 'Change' is the one for obvious reasons," he added, referring to the word which is also his election campaign slogan.

Swift is currently touring the UK as part of the Europe-leg of her Era's tour. She is performing two more shows in London on Saturday and Sunday before returning to the British capital again in August. 

She has already played shows in Edinburgh, Liverpool and Cardiff and will be heading to Dublin next.

The London Mayor's office announced on Thursday that the eight Era's tour performances in London would general £300 million ($380m) for the city's economy.

In the lead-up to Friday's show, the mayor unveiled several murals dedicated to Swift as well as a special Tube map with stations named after songs to mark the tour.