<p>Totally complex submanifolds of a quaternionic Kähler manifold are analogous to complex submanifolds of a Kähler manifold. In this paper, we construct an example of a non-compact totally complex submanifold of maximal dimension of a compact quaternionic Kähler symmetric space, except for the quaternionic projective spaces. A compact Lie group acts on our example isometrically, and this action is of cohomogeneity one. Our example is a holomorphic line bundle over some Hermitian symmetric space of compact type. Moreover, each fiber is a totally geodesic submanifold of the ambient quaternionic Kähler symmetric space and our example is a ruled submanifold. Our construction relies on the action of a subgroup of the isometry group and a maximal totally geodesic sphere with maximal sectional curvature known as a Helgason sphere. Furthermore, we prove that there exist no compact submanifolds of the same dimension that contain our example as an open part, except when the ambient quaternionic Kähler symmetric space is a complex Grassmannian.</p>