\begin{longtable}[]{@{}ll@{}}
\hline
Outer Left\par
 & Outer Right\par
\tabularnewline
\hline
\endfirsthead
\begin{longtable}[]{@{}ll@{}}
A\par
 & B\par
\tabularnewline
C\par
 & D\par
\tabularnewline
\hline
\end{longtable}
 & Regular cell\par
\tabularnewline
\hline
\end{longtable}
