Fellow judges Amanda Holden and David Walliams and hosts Ant & Dec were also on hand at the Waterfront Hall on Saturday (18 January) as the panel began their search for the next big thing.
Hundreds of hopefuls braved the rather rotten weather for their chance to impress the judges and follow in the footsteps of stars like Susan Boyle, Diversity and last year's winner Attraction.
It was the first time auditions have been in Northern Ireland.
The judges travelled in style via Simon's private plane, with Amanda snapping a picture of herself, Alesha and David on the airport tarmac.
"On my way to board Cowell Air and fly to Belfast!" she wrote, adding: "Waiting For God!oh!! Nearly on our way!!!! @AleshaOfficial @davidwalliams (sic)."
Despite the rain on the red carpet, all the judges looked in good spirits. We wonder if they'll look so cheery by the last audition! We suppose it will depend on the talent…
Simon gave us a taster of what we could see when he tweeted: "Hello. I am in Belfast. First day of britains got talent. Have just seen a cat backstage trying to play the guitar!"
Please let that make the final cut!
Aside from seeing a cat trying to play an instrument, Simon also came face-to-face with his biggest fan in Northern Ireland! The brunette turned up to auditions wearing an 'I heart Simon Cowell T-shirt' and got a kiss from the man himself!
All in all, it appears to have been a good start to auditions, with Amanda telling her Twitter followers: "Leaving Belfast now!! We found some gems!"
David added: "Thank you everyone who came to the #BGT auditions today in Belfast. What a brilliant start to the new series."
Open auditions for the show were held last year and now it's time for the judges' auditions, but if you still want to apply you have one last chance. An open audtion is taking place at The Kia Oval in London on 25 January from 9am to 7pm.