American media group Viacom has agreed to purchase Channel 5 from Richard Desmond for £450 million.
He told The Guardian that he had already recouped his investment so he had effectively turned £100m into £550m.
The US group's acquisition includes subsidiary channels 5*, 5USA, the children's TV brand Milkshake and the digital on-demand service Demand 5.
The deal by the group whose profile already includes MTV, Nickelodeon, VIVA and Comedy Central will see Viacom make a major move into free-to-air television in the UK.
Philippe Dauman, chief executive of Viacom, said of the deal: "The acquisition of Channel 5 accelerates Viacom's strategy in the UK, one of the world's most important and valuable media markets.
"Channel 5's momentum is indisputable, with impactful programming, increasing popularity and a growing digital platform."
Desmond purchased Channel 5 from RTL group in 2010 for £103.5m and moved to the channel into the same London HQ as his newspaper and magazine titles. He put the channel and its subsidiaries up for sale in January of this year and was reportedly hoping to get £700m.
The deal with Viacom was more in line with anaylsts forecasts for a sale of £400m to £500m, according to the BBC.
Dauman paid tribute to Desmond's management team at Channel 5 and the work they had done to turn the channel around. He said: "Channel 5's management and employees have done an outstanding job building their brand and we are pleased to welcome them to our team."
Before 2010 the channel had made significant loses but is now on course to make a profit of £70m, according to the Guardian. Dauman added: "Viacom's global resources, technology and expertise will help Channel 5 develop even more compelling programming. In addition, we will introduce our popular content to new UK audiences and create a comprehensive offering for our commercial partners on-air and online."
Channel 5's main news output is provided by ITN.