Here are three sources reporting that Microsoft employee Jerry Nixon announced it at Microsoft's Ignite conference in 2015. They announced the transition to "Windows as a service" model, and it is also reported that Satya Nadella described this as a "new era" for computing.

https://www.theverge.com/2015/5/7/8568473/windows-10-last-version-of-windows

https://www.windowscentral.com/windows-10-may-be-last-version-windows-microsoft-rethinks-operating-system

https://www.bbc.co.uk/news/technology-57443598

I don't have a link to a Microsoft source, or the original video/audio, but the sources are reputable enough that I'm sticking with my original statement.