"And Mum's been going, 'Don't get your hopes up, I don't think you'll win'."
But he did.
Dexter is about to enter Year 11 at Glendowie College and will take classes in photography after being inspired by his aunt and uncle who were both photographers.
"I've been practising a lot, so this is really good."
He said he was left "speechless" after being told of his win.
"That's awesome, just really, really awesome."
Dexter was given a camera for his birthday last month - but now he'll have two to practise his craft with.
Second place was awarded to Doug Crowther, from Tuakau, for his shot of two fledging starlings sorting out their differences beak to beak mid-flight. He won a Canon EOS600D EFS-55IS camera.
And third place went to Justine Brailey who won a Canon EOS1100D EFS18-55 camera for her shot of young Benjamin enjoying a sprinkling from the garden hose during a hot summer's day.
As well as their cameras, the first, second and third place winners took home a Pixma MG8250 printer, a Canon backpack and an SG201A4 paper pack.
During the six-week competition, the Herald received about 9000 photographs from 7000 readers who sent in their best summer shots.