Subgroups of the spinor group containing a split maximal torus. II

In the first paper of the series, we proved standardness of a subgroup $H$ containing a split maximal torus in the split spinor group $\operatorname{Spin}(n,K)$ over a field $K$ of characteristic not 2 containing at least 7 elements under one of the following additional assumptions: 1) $H$ is reducible, 2) $H$ is imprimitive, 3) $H$ contains a non-trivial root element. In the present paper we finish the proof of a result announced by the author in 1990 and prove standardness of all intermediate subgroups provided $n=2l$ and $|K|\ge9$. For an algebraically closed $K$ this follows from a classical result of Borel and Tits and for a finite $K$ this was proven by Seitz. Similar results for subgroups of orthogonal groups $SO(n,R)$ were previously obtained by the author, not only for fields, but for any commutative semi-local ring $R$ with large enough residue fields.