Honda's latest spell in Formula 1 will come to an end in 2021 after the Japanese manufacturer made a shock announcement that will have wide-reaching ramifications.
Not only does it put F1 back down to three power unit manufacturers, a level it has not been at since the start of the V6 hybrid power unit era in 2014, but it also leaves Red Bull facing big challenges to overcome in the short-term future.
Honda confirmed in Friday's announcement that it "communicated our thoughts to Red Bull Racing" in August that it was considering an F1 exit, before it "determined to conclude participation at the end of September".