We know from the photograph in Augustine's box that Grandfather was identical to Alex when he was Alex's age. We also know, thanks to the (small) photo album at
Who is Augustine, what Grandfather looked like in the year 1946, when he would have probably been in his twenties. Now I love Eugene Hütz, but he really isn't the Alex I pictured in the book (which is fine, because I've made a point to think of the book and movie as separate entities).
Therefore, I present to you...
Alex?
And the silhouette from Alex's incomplete info page.