Koi Betta Fish, Male or Female?

I’ve had this Koi betta I bought from a local pet shop a few months ago. I was told it was a Male but just not fully developed yet so I just assumed it was. As I’m looking at other bettas to help my brother and sister get into the hobby I’m starting to think my betta may be a female. Was wondering if anyone with a better eye for this can help!

Thank you in advance!!

 

Beautiful guy you got there. Males tend to be more aggressive and will flare at the sight of another male, females typically don’t pay attention too much to other bettas. Try putting a mirror in front of the little guy and see what he does

 

No doubt a male.

 

I know I'm late to the party but I couldn't resist. He's too cute. I'm curious, though. Has he changed to a darker color yet?

 

Could just be me but I'm thinking female.