Bauer Media, a German-owned private company which is also homes to magazines including Grazia and Heat, confirmed the deal on Wednesday as predicted by MediaGuardian last month.
The loss-making digital radio station was put up for sale by its owner, millionaire entrepreneur and rock music fan Malcolm Bluemel last year.
Bauer bought the station for an undisclosed sum but the company is thought to have paid between £1m and £2m, with the sum likely to be closer to the former than the latter.
You can hear Planet Rock on Virgin Channel 924.