High-intensity running and the broccoli and chicken diet his mum Jenny fed him also helped his dramatic kilo plunge. "Dad [Malfroy School principal Nicky Brell] and mum shared the diet, we've all benefited from it."
Not that Matatia's weight's ever ballooned - he's been a gym junkie since he was 13.
It wasn't only the fitness level of his fellow cast and crew that Matatia lacked - it was on-stage experience.
Although he's a finely tuned musician and singer, he'd never considered musical theatre. He was headhunted for the "right up there" role of Sky.
The way he puts it is he "kinda struck it lucky".
"The producers weren't having much luck finding the right guys for the younger roles, they just weren't auditioning. I was singing with my cousin in Brisbane when friends started blowing up my phone and emails telling me I had to come home and audition. I got out of the car and was told 'you've got the role', I thought 'why not?'."
To our verbal lob that he must have been the answer to the director and producers' prayers, Matatia bats back that they were the answer to his.
"It was something I'd never considered, had no idea I'd enjoy it so much, it's sparked a real passion in me."
He admits that until the show came along he was somewhat rudderless, not having the slightest idea what he wanted to do for "real work".
He was fresh out of Te Kura Kaupapa O Te Koutu where he'd spent 10 years totally immersed in te reo, when one of his dad's mates pointed him towards the about-to-get-off-the-ground musical academy at Waiariki.
"I'd always loved music since I was a little boy. Mum bought me a guitar when I was 13 and I started lessons with Richard Anaru but quit after two years because I couldn't be bothered with the difficult stuff. I now think 'shucks, if only I'd done the hard yards then'."
He turned to the piano and, being a child of the times, taught himself via YouTube.
"I guess I'm lucky my ear hears notes but I don't know what's going on in my brain so my music just kinda happens. At that stage I was quite shy - didn't like to play and sing in front of people."
That reluctance was a hurdle he forced himself to leap over for his music academy audition. He needn't have stressed. After singing The Club, "Stan Walker's version", he was a shoo-in for the top platinum scholarship which funded his fees.
Academic study ran alongside his musical tuition, leading to a diploma in business studies.
"Hopefully sometime in the future I'll go to Waikato [University] and get my degree."
On day one at the academy, led by Richard Anaru, Matatia was handed drumsticks and told a drummer was needed.
"I'd never drummed before, it was a new skill to pick up, I was really chucked in at the deep end working with these amazing musicians."
He and classmates Te Kahurangi Webster, Neihana Mackey-Harrison and Desian Robb joined forces to form the Waiariki Kotete; their "bit of a joke" on the word quartet. Matatia was arranger-cum-bass singer.
"We were singing acapella, harmonising and blending really well, we got to the stage no one knew who was bass, who was tenor, and it was awesome."
The Kotete became sought-after on the local entertainment scene, performing at the Te Arawa Sports Awards, business-dos and Christmas functions.
"We still meet up and jam together."
Matatia also sang in the academy choir and continued his involvement with kapa haka which began at school.
Once graduated "and feeling a bit more confident" he to-and-froed across the Tasman, joining his cousin Ngahere (Nuz) Ngatai and a group of serious musos gigging around Brisbane's restaurants, night spots and corporate events.
"We were doing anything and everything, adjusting different styles to the audiences.
"It was pretty full-on, we could be performing eight hours straight - that's a lot of songs.
"As a group they were very talented musicians and singers. I learned a lot."
As local audiences have discovered, it was Mamma Mia! that was to benefit.
Matatia's tight-lipped about what's to follow.
Hard as we tried to prise it of him, he would only say "it's probably not in this style of work [musical theatre] but people may soon be seeing a little bit more of me".
We hope so, Matatia, we certainly hope so.
MATATIA BRELL
Born: Rotorua, 1993.
Education: Rotorua Primary, Te Kura Kaupapa Maori o Te Koutu, WIT music academy.
Family: Parents Nicky and Jenny Brell, sister Antonia Brell. "I've got a girlfriend but she wouldn't want to be named."
Interests: Music, acting, the gym, fitness, running, "shooting hoops with my mates", "watching lots of films".
Personal philosophy: "You can fail at something you don't love and not take chances by doing something you do love."
