Need help fading outside of ellipse to black

I want to get this image printed on a black t-shirt.

The blue effect on the background of the image, which I want to keep, stretches beyond the outside of the image so if it was printed, you'd see a box around it and it would look ugly on the t-shirt.

A solution, to me, would be to drawn an ellipse around the image and fade the outside of the ellipse slowly to black but I don't know how to do this.

Any suggestions?

 

If you have photoshop you can use the layer mask tool with a black & white radial gradient.

 

You can use the layer mask and add gaussian blur to mask.

 

Dear friend, I understand your issue. I will do that professionally. You can order me this job via : https://www.fiverr.com/clippin_expert

 

This is my way that I'm thinking about this design.