LICENSING QUESTION. I am writing C# code based off of the source code from the Doom 3 engine. It’s not a 1:1 port, just writing code similar to it. Do I need to include a license when I ship my assemblies?

The Doom 3 engine has a GPL v3 license attached to it. Even though my code is not 100% identical, even if converting to C#, do I still need to ship a copy of the original license? This is a commercial project. Not asking because I want to deny anyone of credit, just very unsure.