[Grammar] This pen is my pen. (Is this sentence correct?)

[Sahil Dhankhar]

This is not my homework.

I know that following sentences are correct. -
This is my pen.
This pen is mine.

But is the given sentence also grammatically correct?

This pen is my pen.

 

[emsr2d2]

It's grammatically correct but unnatural. No native speaker would say it.