Make path revealing certain parts of an underneath layer with gradiant

Hi, 

I want to make a quick animation revealing the underneath screenshot of an online shop by creating a path with a transaprent gradient (s. video below, I basically want what i did in photoshop without you seeing the gradiant tool you used in ps)

I hope somebody has an idea for me (since I want to make a video I also don't know if I should do it in pp or afx)

Kind regards, 

Julia Zok