Co-producer Oriwa Hakaraia said she instantly saw star quality in William.
"I think he reflects the character of Wiremu so well. I mean, it's all there in the name.
"He has that energy that you know tamariki bring to a space.
"It's fun, it's unique, it's exciting, so yeah I think those are just some of the reasons why Wiremu was sort of like an obvious choice for us.
"Watching him I was also just blown away," she said.
William began his language journey at Pukeroa Oruawhata Kohanga Reo and he now attends Rotorua Primary School.
Mum Jade Lockwood said she couldn't be more proud and she credits his teachers.
"We wanted to make sure that our children had the opportunity," she said.
"It is a journey that we all travel through together."
Rotorua Primary School kaiako Whaea Layla said William's big break comes as no surprise.
"It's been beautiful to see his te reo journey throughout our school.
"He's a beautiful kid - very talented.
"One thing I loved about William when I was his teacher was he always tried his hardest to speak te reo Māori all the time.
"That's one thing I always encourage with my kids - use as much te reo as you can.
"He's that kid," she said.
William had a few words of encouragement for any young people who have big dreams.
"If your dream is to become an actor you've got to try to do your best, like I did," he said.
"My first audition was Lion King and I didn't get the part so I tried again.
"Try until you get your part," he said.
The premiere of the film will coincide with the Maoriland Film Festival which is happening in Otaki between June 29 and July 3.
