I'm trying to generalize a theorem on $\operatorname{SL}_n(\mathbb Z)$ to the Chevalley groups over $\mathbb Z$. In the theorem, there is a heavy use in the element $e_{1,n}(1)$ where $$e_{1,n}(m)= \begin{pmatrix} 1 & 0 & \cdots & m\\ & 1 & & \vdots\\ & & 1 & 0\\ & & & 1\\ \end{pmatrix}, $$
together with a general element from the Bruhat big cell.

I was wondering if there is a way to characterize $e_{1,n}(1)$ in the general Chevalley groups over $\mathbb Z$?