Max Jerry was “fast-tracked” into Three Years Younger after meeting Megan and Charlie Simpson who started the group in 2016.
They have been chosen by BBC Introducing to open Sunday’s Alcove Stage.
Jerry said the reality would not “sink in” until he saw the crowd.
The group, who describe themselves as from the Suffolk and Cambridgeshire music scenes, were also joined by Inigo Ayesteran last year.Singer Charlie said: “Me and Megan had been performing for such a long time as a duo and we always had in our head this image of how the song should sound with drums and bass and electric guitar and everything we could think of… we just needed the people to help us make that happen.”
IMAGE SOURCE,DJ LAREN/BBCNewcomer Jerry said he was “fast-tracked” into the band.
“I learnt the set in a day,” he said. “I just went to a practice room alone and jammed out.
“Then we had a practice the day after where I initially met Megan and Charlie and then the day before our first gig I met Inigo.
“When I’m on that stage and I’m playing in front of people and I see the crowd, that’s when it will sink in.
When asked about the future of the band Megan Simpson, the older of the two sisters, said: “In five years’ time we are going to be on a big main stage at Glastonbury.”
“I’ve always worried that time is running out… but I have never once thought that we are not good enough for it. I’ve always thought we can do this if we get the right team, the right people behind us, the right support and we put the work in,” she said.