  Let $G$ be a simple algebraic group of adjoint type over $\mathbb{C},$ whose
root system is of type $F_{4}.$ Let $T$ be a maximal torus of $G$ and $B$ be a
Borel subgroup of $G$ containing $T.$ Let $w$ be an element of Weyl group $W$
and $X(w)$ be the Schubert variety in the flag variety $G/B$ corresponding to
$w.$ Let $Z(w, \underline{i})$ be the Bott-Samelson-Demazure-Hansen variety
(the desingularization of $X(w)$) corresponding to a reduced expression
$\underline{i}$ of $w.$ In this article, we study the cohomology modules of the
tangent bundle on $Z(w_{0}, \underline{i}),$ where $w_{0}$ is the longest
element of the Weyl group $W.$ We describe all the reduced expressions of
$w_{0}$ in terms of a Coxeter element such that $Z(w_{0}, \underline{i})$ is
rigid (see Theorem 8.1). Further, if $G$ is of type $G_{2},$ there is no
reduced expression $\underline{i}$ of $w_{0}$ for which $Z(w_{0},
\underline{i})$ is rigid (see Theorem 8.2).
