Facebook completes acquisition of WhatsApp messaging service now worth $21.8 billion

Facebook has closed its acquisition of mobile messaging service WhatsApp in a deal that is now worth $21.8 billion, up from the original $19 billion deal struck, thanks in part to the social network giant's rising stock price since February.

Menlo Park, California-based Facebook said Monday that it has named WhatsApp co-founder and CEO Jan Koum to its board of directors. WhatsApp is by far Facebook's largest acquisition, and bigger than any that Google, Microsoft or Apple have ever done.

The deal's value raised eyebrows when it was announced on Feb. 19, though analysts said it makes sense for Facebook to buy the popular messaging service.

WhatsApp has been growing rapidly, especially in Brazil, India, Mexico and Russia. It has more than 500 million users.