  We establish the $Q \widetilde{Q}$-systems for the twisted quantum affine
algebras that were conjectured in arXiv:1606.05301. We develop the
representation theory of Borel subalgebra of twisted quantum affine algebras
and we construct their prefundamental representations. We also propose a
general conjecture on the relations between twisted and non-twisted types. We
prove this conjecture for some particular classes of representations, including
prefundamental representations.
