Sam Wilkinson, 15, won the TV show two years ago after he wowed judges with some of his own compositions and The Beatles’ Hey Jude in the final.
His performance at Castle Nights was alongside girlfriend Bee Bran, also 15, who was in the island with her famous local musician father Tim.
‘It’s a very unique venue,’ Sam said.
‘The atmosphere was fantastic, the other band playing at the event was great, and thanks to those that organised everything.’
Bee added: ‘The performance went really well, and the venue was amazing.’
The young duo said they would be keen to play in Guernsey again. They have also performed during the Guernsey Street Festival during their holiday.
They made contact with Russ Fossey, head of arts development at the Guernsey Arts Commission, who arranged the appearance at Castle Cornet.
‘We were delighted to have the opportunity for them to perform at the castle,’ Mr Fossey said. ‘They came in really quietly, with no promotion, but it went down really well with the crowd.’
Since winning ITV’s The Voice Kids, Sam said he has been playing gigs, writing songs, been active on YouTube, and even performed at the Royal Albert Hall.
Bee finished in second place winner in the UK National Song Writing Competition in 2018. In February she released an EP called Artificial Ecstasy.