Left 4 Dead 3 in development?

Source 2 also spotted during Valve office tour.

During a recent tour of Valve's offices, a group of Dota 2 players seem to have unearthed evidence that Left 4 Dead 3 and Source 2 are actively in development.

One member of the group snapped a picture (which you can see below, the zoomed in version of the image that came via Neogaf), and both Source 2 (the next iteration of the engine used to power Valve's games) and Left 4 Dead 3 were mentioned on the internal changelog.

Source 2 was confirmed by Gabe Newell last year, so it's not much of a surprise that Valve are working hard on the engine, but Left 4 Dead 3 is a different kettle of fish altogether. Sadly, there was no mention of Half-Life 3 on the changelog, but that hasn't stopped the speculation from rumbling on.