"We really started talking about what it was going to be like to connect everyone in the world.
"It wasn't really until we got aligned on that vision between Facebook and WhatsApp that we actually started talking about numbers and decided to make a deal.
"It's that vision that I think makes the companies such a great fit.”
Former Yahoo! engineer Mr Koum, who co-founded the company with American Brian Acton, said: “We’re excited and honoured to partner with Mark and Facebook as we continue to bring our product to more people around the world.”
Mr Koum confirmed that he will join the board of directors at Facebook.
It is the social network’s largest acquisition to date. It will pay £2.4 billion in cash and £9 billion in Facebook shares.
