Who are the wildcard of Britain's Got Talent, Libby and Charlie?

This week's British Got Talent semifinal saw 10 of the 40 groups advance to the big final on Sunday night – but the judges added a wild card choice to the training.

As in previous years, the jury chose a number that did not qualify in the semifinal to join the numbers that had made it – giving them a chance at the title and place at the Royal Variety Performance.

And this year's happy release is the Libby and Charlie duo, who reached the final after taking their place in the semifinals at the very last minute.

Here's what you need to know about them.

What is Britain's Got Talent Law: Libby and Charlie?

Libby and Charlie are 11 and 12 years old (in fact, Charlie was 12 last Friday, the day he made it into the semifinals live) and the best friends of Liverpool and Manchester.

They originally appeared in the series' seventh series of shows, winning four "yes" judgments from judges for their emotional routine in Christina Perri's A Thousand Years program.

However, the pair was not initially selected when the 40 semi-finalists were chosen. She was unable to access the last semifinal at the last minute after another act, The Brotherhood, retired from the competition.

Charlie even admitted that he was on vacation when news of their place in live broadcasts arrived – and had to hurry back.

"It was about Wednesday [when we found out]Charlie explained. "I was in Greece and I slept on the tanning bed" – with Libby who told Ant and Dec: "I was on FaceTime for Charlie, like:" you have to come now, get on this plane and come! "

What did the judges say about them?

The routine of the pair inspired by Charleston in the semifinals earned them rave reviews from the panel.

"You did two incredible things tonight," David Walliams told them. "You have filled our hearts with incredible joy, skill, commitment and pbadion … and, more importantly, you've made Ant and Dec feel great."

"You two are breathtaking," said Amanda Holden. It was an incredible show, absolutely choreographed. I salute you absolutely for that … fabulous.

They first finished third in their series, losing to Magic Act X, who finished first in the semifinals, and economist Jonathan Goodwin, who took second place.

The British final Got Talent will be held Sunday night on ITV from 19:30.