What’s cooler than a billion dollars? A billion dollars without board approval.

The Wall Street Journal is reporting that Facebook’s acquisition of mobile photo sharing app Instagram was pursued by Mark Zuckerberg alone, with board members notified only hours before the deal was set to close. According to one source, the board "was told, not consulted."

It is the company’s largest acquisition yet—and perhaps ever—according to the Facebook founder and CEO.

Zuckerberg and Instagram founder Kevin Systrom are said to have first met on Thursday, April 5, mere hours after Mr. Systrom secured a $50 million investment round led by venture capitalist firms Sequoia, Thrive Capital, Greylock, and Benchmark. The pair talked for three days before finally agreeing to a deal on Sunday afternoon.

Such deals are usually not made so quickly, nor without a cadre of lawyers and financial assistants present, but Mr. Zuckerberg chose to pursue the deal largely on his own. The report says he was afraid of Mr. Systrom reacting negatively had he been approached through lawyers first.

While the Instagram founder initially sought $2 billion, Mr. Zuckerberg planned to pay largely with stock, and suggested Mr. Systrom “[look] at the value of Instagram as a percentage of the value of Facebook” over time instead.

Although Facebook’s board did eventually vote on the deal, sources tell The Wall Street Journal, the vote was "largely symbolic."