Australian entrepreneurs Alex Tomic and Nik Mirkovic were not yet 21 when they came up with an idea that would rank them among their country's youngest self-made multimillionaires and put their names on the lips of celebrities from Kylie Jenner to Conor McGregor.
The moment came at dinner one evening in 2014, shortly after Tomic had dropped out of his first semester of his undergrad studies. Within hours, the best friends had decided to pool their savings — a combined 20,000 Australian dollars (around $15,000) — and give it a go.
Three years on, their business has surpassed 50 million Australian dollars (almost $40 million) in sales, and last October their estimated $35 million joint fortune earned them the title of youngest new entrants on the Australia Financial Review's Young Rich List 2017.
Tomic and Mirkovic, now 24 and 23 respectively, are the guys behind HiSmile: the Australian teeth whitening start-up that shot to success on the back of social media marketing.
The entrepreneurs' idea was born out of their observations of the retail industry at the time, and how online influencers were becoming increasingly important for brands.
They wanted to come up with a product that could capitalize on the trend, and identified the dental care industry as a point of attack.
"Lo and behold we had a bit of a discussion at the dinner that sort of extended, it was a couple of hours, and we came up with the concept of HiSmile and entering the space of oral cosmetics," Mirkovic told CNBC Make It.
"We felt that that was a static space, static industry, and one that we could really attack and build a brand in," he added.
The pair, who both live on Australia's Gold Coast, wanted to create something that consumers were proud to associate themselves with, and soon came up with their flagship product: a do-it-yourself teeth whitening kit aimed at 15 to 25-year-old social media users.
Retailing at $59, the set includes a mouth tray, a LED light and three gel tubes.
They then "made it beautiful," said Tomic, and sent it to micro-influencers — social media users with a burgeoning following — to gauge feedback.
"We never wanted to throw money at influencers from the start," explained Mirkovic. "So we started with micro-influencers, influencers with 1,000, 2,000, 3,000 followers – people that normal brands wouldn't really see influencing."
"After they shared their experience with the audience, we saw the proof of concept was there, we saw that people actually loved the product."
Within 18 months the duo had raked in more than 10 million Australian dollars in sales and decided to put more budget behind their marketing strategy, targeting higher profile personalities, including fighting titan Conor McGregor.
A major breakthrough for the pair came in 2016, when they signed up Instagram icon Kylie Jenner.
They had been working closely with Jenner's mother, Kris Jenner, who at that time was managing one of HiSmile's other Instagram influencers.
"Success came relatively quickly, and we were like, 'Okay, let's start talks about Kylie,'" recalled Mirkovic.
Jenner's then-75 million Instagram followers, many of them HiSmile's target demographic, made her an ideal advocate for the brand. But the guys spent several months discussing the deal to make sure it would be a genuine endorsement.
"Obviously she's got to actually enjoy and believe in the brand and the product and what we're selling," said Mirkovic.
Since then, the business has grown rapidly, amassing close to 1.7 million likes on Facebook and 749,000 followers on Instagram.
The duo said they have no regrets about betting on the company with their own cash.
"Starting with that 20,000 (Australian dollars), it was making the wise decisions and understanding where to put it," said Mirkovic.
"People see that as a risk, putting that money towards starting something, but you look at what you can spend 20,000 on, or 10,000 each, that isn't even a waste of money," he added. "It's education for us."
Today, Tomic and Mirkovic remain the sole investors in HiSmile, pumping much of their fortune back into the business.
"From day one, we've made the right decisions, and we've doubled down and invested back into ourselves," said Tomic.
By the end of 2018, the guys hope to hit 100 million Australian dollars ($77 million) in sales. They said they have no intention of taking on external investors.
"This isn't something we're in for just the next three years. We're in this for the next 50 to 100 years," said Tomic.
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—CNBC's Camille Bianchi contributed to this report.