Guernsey 400m runner Cameron Chalmers says he was surprised to be called up by Great Britain Under-20s for Sunday's Loughborough meet.
The 18-year-old ran a personal best 48.34 seconds at Guernsey's Island Games Selection earlier this month.
He is one of six athletes selected for the 4x400m relay event.
"I didn't expect to run that quickly this season so it was a surprise, and I knew it gave me a chance to get picked," Chalmers told BBC Guernsey.
"For the last week I've been sitting around with my fingers crossed, just waiting to hear the news."
The teenager is the first Guernsey athlete to be named in a GB squad at any level since Lee Merrien in 2012.
He will form part of a 52-strong GB team which will compete at the Paula Radcliffe Stadium on Sunday.
"It's really exciting for us as a club. To put into context what he's done, he ran 48.3 seconds at Footes Lane - at that age I had the record for that age group and it was 49.2," said Guernsey team manager Tom Druce.
"I ended up running the in the low 46s so he's now got to be thinking he has the potential to really kick on and run maybe 45s, which is GB senior scene standard."
Chalmers has also been included in Guernsey's Island Games squad, where he aims to win gold.
GB Under-20s 4x400m team: Cameron Chalmers (Dale Garland; Guernsey), Freddie Owsley (Alastair Abrams; Bristol & West), Nick Petrou (Baron; Leeds City), Joseph Reid (Matt Elias; Manx), Daniel Rowden (Richard Thurston; Woodford Green Essex Ladies) and Lee Thompson (Peter Moore; Rotherham)