1. Initial Process: Facebook recruiter contacted via linkedin in late April. Call with hiring HR scheduled in 1st week of May.
2. Call with HR: HR person was very humble. Had a little discussion about profile, skills and other preferences. HR briefed me about the complete interview process and provided some useful resources to prepare for interviews. First telephonic round was scheduled after a month.
3. 1st technical : 45 mins allocated for this round. It had two medium complexity questions that needed to be discussed and solved on whiteboard. It was clear.
4. HR called to congratulate and scheduled next rounds after 6 weeks, enough time to get prepared. 4 rounds were scheduled. To help prepare better, Facebook organizes con-call where all the aspirants can join and a team from Facebook guides about how we shall do the interviews. Also, a one-on-one call was scheduled with an employee, where we can ask any question about interview experience, preparation material, life and projects at facebook, or London.
5. All the 4 interviews were scheduled for 45 mins each.
6. 2 were coding rounds. Both containing 2 questions each of medium complexity. due to NDA, cannot tell the questions here. Both went well.
7. 3rd was System design question. It was designing of dropbox. It was a good discussion roung. Facebook wants us to talk more here.
8. 4th was behavioural round. Mostly questions are available on Internet. Interviewer was basically trying to catch the leadership experience. As I was SDE2, I didn't have fair experience at that side. Rest of the part went well.
9. In about a week, recieved a detailed feedback from HR. They were 90% satisfied. But Facebook never takes a bad hire even if it is 10% negative. She highly motivated me to apply again after sometime as they only wanted a person at lead level position.

P.S. : People take rejection as bad thing. But It has been one of the very proud moment for me. Getting a call from FAANG, is in itself an achievement. And, remember....
Now I have reached one of those, it's just that I am at the door, and no one knows when that gate can open and I will be on the other side very soon.
Just keep preparing and stay motivated.!!!