Former Fortress hedge fund manager Michael Novogratz told a conference Tuesday that the digital currency market will be a wild roller coaster ride full of froth and shady behavior.

“I think this [crypto] is going to be the biggest bubble of our lifetimes by a longshot,” he said at the CoinDesk Consensus: Invest conference in New York. “To be fair, this is a bubble and there’s a lot of fraud mixed in. We look at tons of projects. And some get funded, and they literally look like Ponzi’s. There’s a lot of froth and fraud in something that’s exciting as this.”

Novogratz’s comments come a day after he gave an aggressive price forecast for bitcoin next year.

“Bitcoin could be at $40,000 at the end of 2018. It easily could,” Novogratz said Monday on CNBC’s “Fast Money.” “Ethereum, which I think just touched $500 or is getting close, could be triple where it is as well.”

Novogratz believes the ride to his price targets will not be smooth.

“There will be wild crashes in it because you’re going to get to levels so far ahead of where the technology’s at. It makes investing really, really exciting, but difficult,” he said at the conference.

The price of bitcoin rose 1.4 percent to $9,870 on Tuesday, according to CoinDesk. The digital currency is up more than 900 percent so far this year.

Novogratz is formerly a macro hedge fund manager at Fortress Investment Group. He is planning to launch a $500 million digital assets fund through his new firm, Galaxy Investment Partners.