Live feed delivery

Design the real-time delivery of new posts to followers' live feeds for a social network where most users have hundreds of followers but a few celebrities have 100M+. When a user posts, their followers who are currently online should see it appear in their feed within seconds. The fan-out-on-write approach (push the post into every follower's feed) is great for normal users but catastrophic for a 100M-follower celebrity. How do you deliver new posts to live feeds for both cases without melting on the celebrity case?