Companies with a founder as chief executive were 25% more valuable than public companies with no significant family control, Villalonga found.

FORBES: The Kochs' Crazy Dividend Policy Is Normal For Family-Controlled Firms

The choice of buyer has strengthened speculation that Mr Middelhoff and Juan Villalonga, Telefonica's boss, plan to forge an ever-tighter German-Spanish axis.

ECONOMIST: Bertelsmann

The Spanish government blocked a previous plan for Telefonica to merger with the Netherlands' KPN, prompting the resignation of chairman Juan Villalonga.

BBC: BT 'considers Telefonica merger'