The judge spoke of his surprise to hear that semi-final winner Ryan O'Shaughnessy had not made it through to the latter stages of the Irish programme.
He stated: "They didn't put you through? Their loss is our gain."
O'Shaughnessy was at one point axed from Britain's Got Talent due to his contractual conflict with The Voice of Ireland and Universal Music.
However, he was later allowed to compete in the show after Universal freed him from the contract.
Cowell later added: "Even though I was teasing the other show, Universal Records were very kind with letting you out of your contract, so thank you."
Speaking about O'Shaughnessy's performance, he said: "You are believable. Your lyrics make sense, I listened to the lyrics. You're a brilliant songwriter and a brilliant singer. Maybe you can be the dark horse in this competition."
Ryan O'Shaughnessy joins Aquabatique, Jonathan & Charlotte, Ashleigh & Pudsey, Only Boys Aloud, Loveable Rogues, Nu Sxool, Sam Kelly, Kai & Natalia and Molly Rainford in the final.
Britain's Got Talent continues on Saturday (May 12) for the final, airing at 7.30pm on ITV1.
Watch Ryan O'Shaughnessy perform on the Britain's Got Talent semi-final below: