Broadcaster ITV has agreed to buy Friends Reunited, the website which has 15 million users and brings together old school friends, for £120m ($208m).
ITV hopes the deal will boost its online presence
The website has the UK's eighth-largest online presence - and profits have risen since the firm expanded to offer genealogy and internet dating services.
ITV said it would pay an extra sum of up to £55m in 2009, according to Friends Reunited's performance.
The deal will allow ITV to "strengthen significantly" its online presence.
Husband-and-wife team Steve and Julie Pankhurst, who set up the website with their business partner five years ago, are set to net about £30m from the deal.
Mr Pankhurst said the business was now "all grown up - it is time for my wife Julie and I to let go knowing it is in safe hands".
After the site's launch in 2000 it became a full-time job for the Pankhursts and business partner Jason Porter.
The Pankhursts gave up the day-to-day running of the site in 2003 but retained a stake in the business.
They funded expansion through a management buy-in and brought on board ex-Financial Times executive Michael Murphy.
ITV wants to team up the website with ITV.com in areas such as dating, recruitment and classifieds.
Created by the merger of Carlton and Granada, ITV controls more than half of the UK television advertising market.
Jeff Henry, director of ITV Consumer said: "The acquisition of Friends Reunited is also a key step in the delivery of our strategy to drive new revenue streams for the company."
The company hopes to have 50% of its revenues from outside its ITV1 channel by 2012, including contribution from mobile phones, online and other new media.
It said Friends Reunited would be maintained and developed as a separate web presence, but the management teams of the site, ITV.com and ITV Local would be integrated.
The websites will feature links to each other.
ITV has high hopes for the Genes Reunited strand within Friends Reunited. The site, which allows people to trace their family tree, has 46 million registered members.