You can host the .NET runtime in an unmanaged application and then load the managed library into it. However, since you are so eager to find a fast solution - rewriting it in C++ is the much better way to go. Hosting the .NET runtime will result in a performance and memory penalty.

However, if you want to take a look at the other solution, this article may be interesting for you. You can also try searching for keywords like "hosting .net runtime in an unmanaged application" or "loading a managed assembly in an unmanaged application", etc.