• by Mark Walsh  @markfwal, October 6, 2014

Facebook on Monday formally closed its acquisition of mobile messaging service WhatsApp, but the final price rose $3 billion to about $22 billion because of the higher value of the social network’s stock since the deal was announced in February.

In a document filed today with the Securities & Exchange Commission, Facebook confirmed that WhatsApp has become a wholly owned subsidiary of the company, and that WhatsApp co-founder and CEO Jan Koum has joined its board.

Koum — like Facebook CEO Mark Zuckerberg — will receive an annually salary of only $1, but will get almost $2 billion in stock that vests over a four-year period as an incentive for him to remain with the company.

Facebook sent ripples through the tech industry when it revealed in February it planned to buy WhatsApp, a start-up with no measurable revenue, for $19 billion in cash and stock — easily the biggest deal in the company’s history. Since then, WhatsApp has grown from nearly 500 million to more than 600 million active users.

The acquisition was cleared by the antitrust authority of the European Union last week, and by the Federal Trade Commission in April. But the FTC warned that Facebook can’t use data about WhatsApp users for advertising purposes without their explicit consent.

WhatsApp remains ad-free, with Koum and Zuckerberg agreeing at the time of the initial announcement that advertising wouldn’t be the right approach to monetizing the app. Currently, WhatsApp allows users to download and try the app for free for the first year, and charges 99 cents per year thereafter.

Facebook paid $4.59 billion in cash and 178 million shares of its stock for WhatsApp, along with 46 million of grants in restricted stock units for WhatsApp employees that will vest over four years.

At Facebook’s opening share price Monday of $77.17, the deal comes to about $21.8 billion.