The broadcaster was expected to make a loss after having bought the site for an estimated £175m in 2005.
Nevertheless the sale price is higher than previous estimates of £15m.
Friends Reunited was launched in 2000 aimed at bringing old school friends back in touch. The sale includes its sister site Genes Reunited, which was launched in 2003. Together with Friends Reunited Dating, the group attracts three million unique users per month.
The acquisition of the Friends Reunited sites will create Britain’s leading genealogy business by bringing together Genes Reunited, findmypast.com and ScotlandsPeople in partnership with General Register Office for Scotland, the National Archives of Scotland and the Court of the Lord Lyon.
Brightsolid is an online business owned by DC Thomson, which publishes Beano and Dandy.
The completion of the deal is subject to clearance by the competition authorities.