Exceptional twin buildings of type C2 : a contribution to the classification of twin buildings

We provide a classification of affine twin buildings of type C2tilde having at least one exceptional residue with one exception in the case E7 in characteristic 2. Relying on the main results of [TW], [W09] and [MPW] we settle the uniqueness. The existence part is settled by refining and adapting the theory of descent in buildings developed in [MPW] to our specific situation.