Paul won the first ever series of Britain's Got Talent over a decade ago now in 2007.
On Monday night, he appeared on America's Got Talent: The Champions, representing the UK.
The brand new series features acts from Got Talent series across the world, competing together to be crowned the ultimate champion.
Opera singer Paul performed Caruso for the judges, including Simon Cowell.
And he won the public vote, becoming the second act from Britain's Got Talent to make the final together with Susan Boyle.
Speaking before his performance, Paul recalled his first audition for BGT back in 2007: "I flipped a coin and decided if it landed on heads I'd do the audition. Thankfully the coin landed on heads and it changed my life.
"I walked onto that stage as a nobody and left it as a somebody."
Simon told him: "You define what this show is meant to be, which is people with extraordinary talent that just weren't given a chance."
Also through in the third heat was singer Angelica Hale. Other acts who performed on Monday night included two more former Britain's Got Talent stars: Extreme Rollerskating Duo Billy & Emily and Illusionist Darcy Oake.
They were eliminated together with Magician Jon Dorenbos, DJ Arch Jnr singer Prince Poppycock, Sideshow Duo Ryan Stock & AmberLynn, comedian Samuel J. Comroe and stand up Tom Cotter.
Last week's second heat saw eExtreme Knife Throwers Deadly Games and opera singer Cristina Ramos make it through while the opening saw Susan Boyle receive Mel B's golden buzzer directly after her performance, seeing her through to the finals, along with comedian Preacher Lawson.
Other acts still to compete for Britain's Got Talent include the most recent champion, Lost Voice Guy.
More former BGT contestants appearing on the show including miniature magician Issy Simpson, and pianist Tokio Myers.
The show airs on NBC in the States on Mondays and on Netflix in the UK from Wednesdays.