Github Hosted Site -- How to hide the github.io with a custom domain?

I have a custom domain (through Namescheap) with the content hosted by Github (nameservers pointed to Cloudflare to get the SSL certificate).

Superficially, the custom domain appears everywhere. On occasion, though, I notice the .github.io makes its way through in some shape or form. An example of this is sending a URL through Snapchat ---as you can see the site shows up primarily identified as a github.io site.

Is there a way to fully remove the github.io portion/identification for all applications?

Extra Info: Github recognizes the custom domain under 'Github Pages' with its "Your site is published at http://..."