Facebook has announced that it has finalised the acquisition of WhatsApp for $19bn (£11.9bn, €15.1bn) adding founder of the messaging service Jan Koum to its board of directors.

The finalisation of the deal comes just three days after the European Union approved the deal, one which had already been given the green light by the Federal Trade Commission (FTC) in the US.

However, the actual price of the deal is now slightly higher than the original $19bn figure, and could be almost $22bn as the price of Facebook's shares have risen significantly.

The deal, which was announced back in February, is one of the biggest in the technology sector in recent years, dwarfing the social network's $1bn acquisition of Instagram in 2013 and the $2bn acquisition of virtual reality gaming company Oculus VR in March 2014.

As well as becoming a member of Facebook's board, Koum will get a nominal salary of $1-per-year, but before you begin feeling sorry for him, he will also received almost 25 million restricted stock units if he stays at the company for four years. Those RSUs at current market value are worth over $1.9bn.

The popular messaging service announced in August that it had reached 600 million users, closing in on the over 1 billion users which Facebook claims.

Facebook's plans for the app post-acquisition are unclear at this stage, especially considering it has its own messaging app - Messenger - which offers very similar services.