who advised that transaction
edit: $12bn in stock, $4bn in cash, and $1bn breakup fee
AND $3bn in restricted stock units after four years, under assorted terms and conditions - per WSJ and others.
Your question is a good one. NYT sez "Corporate advisers played some role as well. Michael Grimes, the Morgan Stanley banker who orchestrated Facebook’s flawed initial public offering in 2012, was this time on the other side of the table, advising WhatsApp on its sale" but they don't say who advised FB. Grimes, wow. How happy could FB even have been ever to see him again...
Update: OK, WSJ has this: "Facebook was advised by Allen & Co. LLC and Weil, Gotshal & Manges LLP; and WhatsApp was advised by Morgan Stanley and Fenwick & West LLP. "