TheWrap is reporting that Christopher Nolan has begun to select the leads for his upcoming film Dunkirk by casting newcomer Fionn Whitehead in one of the two main roles. Insiders state Nolan has been testing young actors for weeks, many of whom remain largely unknown, as we initially reported back in December. Whitehead has a limited history on camera, with his only role being in the three-part horror-drama Him on ITV, but is a part of the National Youth Theatre in the UK. Tom Hardy, Kenneth Branagh, and recent Academy Award winner Mark Rylance are still set to fill out the rest of the ensemble cast.