Greg Isenberg took to his Facebook profile on December 3 to tell his family and friends the inevitable: StumbleUpon was formally shutting down 5by.

It was the startup Isenberg founded in Montreal and eventually sold to the San Francisco-based mega-company.

“Today 5by was shut down. We built one of the most popular video discovery apps. Hell of a ride,” Isenberg wrote.

That was it. There was no official explanation by StumbleUpon in its email to 5by users, but those close to Isenberg knew the deal. Over a year after being acquired, Isenberg left StumbleUpon and was already starting on his next big consumer app.

Still, the day’s events hit him hard. Isenberg sat down with MTLinTech for an exclusive interview.

“On one hand when you sell your company, and you put the control in someone else, part of me said ‘alright, its over.’ It was over when we signed the term sheet,” he said. “The other part of me saw that tens of millions of video plays were on our platforms. I literally got hundreds of emails from users today saying “wtf?” And it’s sad.”

And that was that.

Founded in 2012, 5by scoured the internet for the best videos, and hand-delivered the ones users wanted to watch through intelligent algorithms, all for free. StumbleUpon acquired it in September 2013 and relaunched it about a year later as an app for chatting about videos with friends. The base technology, or the ability to get curated video plays, still runs strong on StumbleUpon.

The sale wasn’t exactly easy for Isenberg, 26, who sold the company at just 24. Before founding 5by he had already ran a successful web agency and was a partner and investor in Wall Street Survivor, the world’s most popular stock market simulation game.

The experience of leaving Montreal ended up being a heartbreaking affair after he sold to StumbleUpon and packed up for San Francisco. It was why he wrote a popular Medium post at the time explaining his departure.

Still, Isenberg and his team forged ahead. The CEO said he grew immensely after his time in San Francisco. He called it ‘levelling up.’

“I grew in almost every area as a founder, whether it be product development, design, connecting with people, understanding the legality of things, doing deals, reading people, speaking, everything,” he said.

A day in San Francisco, he said, is like 100 days spent in a smaller startup market. He compared it to tennis. He loves playing tennis, but he doesn’t want to play someone who’s worse than him. Moving to SFO meant surrounding himself with a lot of people who had achieved much more.

“It makes you work harder because everyone else is more successful than you. The guy next to you sold his company for $50 million, the guy on the other side just raised a lot of money, and obviously that’s going to level you up,” said Isenberg.

But while at StumbleUpon, Isenberg felt the ‘itch.’ He wanted to create something brand new again.

First he thought he was going to take a year off and travel the world, but that didn’t happen. In fact, he lasted two months before he got bored. An that’s how he arrived in Montreal in early December chatting with MTLinTech at a small bar tucked away on rue William in Griffintown.

Here’s what we learned from Greg: his next project is going to be big. He’s starting it with the same founding designer he’s always worked with, Marius Ciuchete Păun, who now splits his time between San Francisco and Vancouver. It’s going to be a consumer-social app that “millions of people are going to use to communicate daily.”

Isenberg said it’ll be just like the other products he’s released: a viral product with no revenue model.

“The Facebooks, the Twitters, the LinkedIns: That’s my goal, to build something mainstream. I want to meet someone on a plane and find out they use the app every day and that it makes their life better,” he said.

Isenberg was vague about the specifics of his new project, but he referenced the fact that the big four messaging apps have now eclipsed the big four social networks in monthly active users. Perhaps it was the writing on the wall back in 2014 the day Facebook bought WhatsApp for $16 billion.

He’s ready and willing to hire Montrealers (or anyone else for that matter) for his new project, which will be based in San Francisco.

“But they have to be the best,” Isenberg warned. “I’m serious: they have to be incredible at what they do.”

Having founded a startup in Montreal that was acquired, Isenberg also wasn’t afraid to talk about how he sees the Montreal ecosystem. He’s been known for acting hard on Montreal, having argued in the past that it isn’t anywhere close to a premier startup city, like New York or San Francisco.

Speaking with MTLinTech, he was perhaps even more forceful in those views.

He’s proud of the Luxury Retreats, the Frank & Oaks, the BusBuds, Lightspeeds and more, but Isenberg wants to see more from Montreal companies. He feels Montreal has the biggest competitve advantage over any other city in North America in terms of starting a company, referencing the city’s beyond-wild ratio of university students per capita. The rent is perennially low for sizable apartments in great parts of town, and the cost of doing business is low.

I’m in Montreal and people here are saying the scene is amazing and things are off the chains. But lets be real: we need more billion-dollar companies. Hootsuite is a billion dollar company in Vancouver, Toronto has Kik and Montreal has Lightspeed, which is great. But I see a ton of raw talent, I see a great quality of life and it’s cheap to build things, so honestly, I expect more from the Montreal community. I expect more billion dollar companies.

But Isenberg himself could have continued his own company in Montreal, but he chose not to.

“Nexology‘s founder Claude Theoret told me a great quote by Mordecai Richler. It was something like, ‘every great Quebecker has left and come back.'”

Only time will tell if this entrepreneur will make his great return to Montreal one day.