Modal dialogs on mobile – Back button

I have one site where I have a little Gallery. Clicking on the image displays a description of the team member and additional image(s).

On a regular desktop I was thinking about implementing the additional information with a PopUp (or some kind of Lightbox). Which is somehow fine cause the user clicks either the X or press the ESC key. And the dialog is closed.

On a mobile device the conent will be displayed same style. But due to the limited screen size and the ammount of content in the PopUp this blocks more or less the whole screen. Sometimes it doesn't even fit on a screen and the user needs to go up and down.

Now the major question is how to close this popup. On a mobile device there is no ESC key. If the user doesn't find easily the close button (s)he closes it with the back button. But using the back button means as well leaving the web page and returning to the previous one.

Any ideas how to display the additional information properly?