Non-classical hyperplanes of finite thick dual polar spaces

We obtain a classification of the non-classical hyperplanes of all finite thick dual polar spaces of rank at least 3 under the assumption that there are no ovoidal and semi-singular hex intersections. In view of the absence of known examples of ovoids and semi-singular hyperplanes in finite thick dual polar spaces of rank 3, the condition on the nonexistence of these hex intersections can be regarded as not very restrictive. As a corollary, we also obtain a classification of the non-classical hyperplanes of DW(2n - 1, q), q even. In particular, we obtain a complete classification of all non-classical hyperplanes of DW(2n - 1, q) if q is an element of {8, 32}