Can I add a 10.3 ArcGIS Server to a 10.2 site?

[RoyceSimpson]

I'm trying to add a 10.3 AGS to an existing 10.2 site with no luck.  I can create a new site for the new 10.3 AGS but fail at joining it to the existing 10.2 site.  I get an error that says that the existing site thinks that AGS is not running on the new 10.3 server. 

I've looked here for guidance but it doesn't indicate one way or another:

Compatibility of ArcGIS 10.3 for Server with earlier versions—Documentation | ArcGIS for Server

[TobiasFimpel1 · Accepted solution]

The documentation at Existing ArcGIS for Server users—Documentation | ArcGIS for Server states:

In a multiple-machine site, can some of my GIS servers run 10.3 and others run an earlier version?

No. In order for your site to function correctly, all GIS server machines need to be at the same update version. You can upgrade your GIS servers at the same time or sequentially. If you have ArcGIS Web Adaptor configured with your ArcGIS Server site, you will also need to update Web Adaptor to the same update version

[RoyceSimpson]

Thanks, that's the documentation I was looking for.