Here is a video of one of Forge World’s studio display boards for Games Day UK 2013.
With the Emperor’s Children in front of them and Iron Warriors engaging them from the rear, Ferrus Manus and the Iron Hands Legion find themselves encircled and betrayed on Isstvan V. The video above shows many of the details that were incorporated into the display, including the fateful duel between Primarchs Fulgrim and Ferrus Manus.