  We study the influence of strong spin-orbit interaction on the formation of
flat bands in relaxed twisted bilayer WSe$_2$. Flat bands, well separated in
energy, emerge at the band edges for twist angles ($\theta$) close to 0$^o$ and
60$^o$. For $\theta$ close to 0$^o$, the interlayer hybridization together with
a moir\'{e} potential determines the electronic structure. The bands near the
valence band edge have non-trivial topology, with Chern numbers equal to +1 or
$-$1. We propose that this can be probed experimentally for twist angles less
than a critical angle of 3.5$^o$. For $\theta$ near 60$^o$, the flattening of
the bands arising from the K point of the unit cell Brillouin zone is a result
of atomic rearrangements in the individual layers. Our findings on the flat
bands and the localization of their wavefunctions for both ranges of $\theta$
match well with recent experimental observations [1,2].
