Richard Desmond, owner of the Daily Express, has bought Channel Five from RTL for £103.5m.
RTL confirmed on Friday that the deal with Desmond's Northern & Shell has been closed with immediate effect.
Gerhard Zeiler, the chief executive of RTL, said "a recovery in the UK TV advertising market meant now was a good time for it to sell" and that the deal was based on a fair evaluation of Five.
Desmond, who also owns a set of porn channels, is keen to invest in Five's TV content and expand its entertainment offering. He is expected to introduce more celebrity programmes and may also try to bring Big Brother, which is in its last series on Channel 4 to Five.
While the purchase would make Desmond the first individual to own a UK national terrestrial broadcaster, it is likely that he will face investigation by Ofcom as well as by MPs in the House of Commons culture committee. They may seek assurances from Desmond that he will not fill Five's schedule with "tabloid TV" shows.