Honda's decision underlines the complex and sensitive situation faced by F1 as it considers how to move forward with a new engine formula from the middle part of the 2020s.
Renault has indicated that it is willing to supply engines to Red Bull Racing and AlphaTauri after Honda pulls out of Formula 1 at the end of 2021. "Toward this end, Honda made the decision to conclude its participation in F1".
McLaren-Honda slowly improved over the following season, but 2017 proved just as bad as 2015 and the two brands parted ways.
With the McLaren Honda proving woefully unreliable and significantly slower than rivals, while many pointed to the sheer complexity of the formula for why Honda struggled to get its Power Unit up to scratch, the laborious process of doing so quickly strained relations with McLaren and earned it a wave of negative publicity from Fernando Alonso's often brutal comments in the media. AlphaTauri - previously Toro Rosso - also have a single victory this season courtesy of Pierre Gasly. Honda enjoyed 67 wins with those two teams alone.
Despite Honda's future retreat from the sport, Red Bull team boss Christian Horner said the energy drink company remained committed to F1.
From next year Mercedes will have four teams and Ferrari three, while now Renault's only commitment is to its rebranded works Alpine outfit.
Honda will quit Formula 1 at the end of 2021, which is the final year of the motorsport's current technical regulations.
Although the decision is a surprise, the motivation won't be.
The combination wasn't successful and their partnership ended after three race seasons, with Honda then supplying Alpha Tauri for a year before striking a deal with Red Bull as well.
Honda has set itself a goal of becoming carbon neutral by 2050 and as a result plans significant investments in the areas of battery- and fuel cell-electric technology.
As it stands - short of developing another engine by itself or with another outside firm, such as Cosworth - it means Red Bull will now need to convince one three major on track rivals to get use of its engines, no doubt a sobering prospect for a team that has a couple of times been a thorn in the side for each for various reasons.
However, what Honda described on Friday as "a once-in-100-years period of great transformation" for the road-car industry has seen a huge shift in focus towards electrification, as manufacturers seek to respond to the challenge of the climate crisis and legislative restrictions on internal combustion engines in many countries. Given the nature of the departure from Renault, a likely unwillingness from Mercedes to supply its main rival, and Ferrari's recent woes, it could have major consequences for the teams - and the sport.