Java file removed from classpath(?!) Follow

Hello there,

By some "unknown" reason, one file of my project is not being recognized anymore as a source file, and as you can see in the attached picture, the file's icon also changed. I tried to associate it back with a "java editor" but no success. When I try to open it, an empty "editor" is open, but without the code.

The code still there (I can see in other editors), but intellij is not recognizing it and removed it from the classpath. 

How can I fix this? and What happened here?

Thanks!