Online news and lifestyle site Buzzfeed is taking over HuffPost in a deal that brings together two of the most high-profile digital media firms.
Seller Verizon Media will become a minority shareholder in Buzzfeed as part of the deal and invest in the combined company.
The two firms will also join up for advertising and sharing content, a partnership they said would "create new revenue opportunities".
The price was not disclosed.
Buzzfeed chief executive Jonah Peretti will lead the combined business. He co-founded HuffPost, formerly known as the Huffington Post, in 2005 with publisher Arianna Huffington and started Buzzfeed a year later.
HuffPost rose to prominence during the George W Bush presidency as a site for liberal bloggers, many of whom contributed for free.
Buzzfeed made its name creating content like listicles and quizzes, which drew young audiences. It also brought on reporters for its news site.
But digital media firms have struggled to draw online advertising dollars away from tech giants such as Facebook and Google. In recent years, Buzzfeed and HuffPost have both shed staff. In May, Buzzfeed closed its newsrooms in the UK and Australia and slashed staff pay.
Mr Peretti said the new deal would increase Buzzfeed's heft, by adding HuffPost readers to its audience and allowing it to tap into Verizon's ad network.
HuffPost is expected to remain a standalone brand, alongside other Buzzfeed sites, including Tasty and Buzzfeed News.
A spokeswoman for Buzzfeed declined to comment on the possibility of job losses triggered by the tie-up.
Verizon Media is part of a US telecom giant, which is known primarily for its pay-TV and mobile phone service. It acquired HuffPost in 2015 when it bought AOL for $4.4bn (£3.32bn), later combining it with Yahoo.
Just a few years later, it wrote down the value of the properties by nearly $5bn.
"While considering opportunities to work together, naturally, Jonah and I also discussed the property he co-founded, HuffPost," said Verizon Media boss Guru Gowrappan.
"We quickly realised BuzzFeed's strategy would complement HuffPost's roadmap, injecting it with new energy and growing the brand into the future.
"We are deeply invested in the continued success of HuffPost and I couldn't think of a better partner to take HuffPost to the next level."
Tough times for new media
A few years ago companies like BuzzFeed and HuffPost were growing fast.
The business model was simple. Produce viral content aimed at younger, online savvy audiences and cash in on online advertising revenue.
That hasn't been as lucrative as they would have hoped.
Ads on digital news stories can actually be quite a clunky way to advertise - less focussed than many advertisers would like.
So Facebook and Google, which offer incredibly bespoke targeting, mop up a massive percentage of online advertising. More than half of all the money spent on online advertising is with these two companies.
Many smaller digital media companies were laying off staff even before the pandemic. Covid-19 has inflamed these problems. People, stuck at home, are clicking more, but advertisers have been cautious.
That's left companies that were seen as revolutionary only a few years ago trying to work out how to survive.
This takeover should be seen in this context - the latest attempt to find a better way of making digital media work financially.