Conversation so far:
who is going to be in the 2018 royal rumble
Contestants of Royal Rumble 2018 include Kalisto, Gran Metalik, Lince Dorado, Luke Gallows, Karl Anderson, Shinsuke Nakamura, Asuka, and Nikki Bella.
how many matches were at the 2018 royal rumble
Nine matches were contested at the event, including three on the Kickoff pre-show.

Question: which royal rumble was this
Self-contained rewrite: which royal rumble was 2018