  Pasquier and Perrin discovered that the ${\rm G}_2$-horospherical manifold
${\bf X}$ of Picard number 1 can be realized as a smooth specialization of the
rational homogeneous space parameterizing the lines on the 5-dimensional
hyperquadric, in other words, it can be deformed nontrivially to the rational
homogeneous space. We show that ${\bf X}$ is the only smooth projective variety
with this property. This is obtained as a consequence of our main result that
${\bf X}$ can be recognized by its VMRT, namely, a Fano manifold of Picard
number 1 is biregular to ${\bf X}$ if and only if its VMRT at a general point
is projectively isomorphic to that of ${\bf X}$. We employ the method the
authors developed to solve the corresponding problem for symplectic
Grassmannians, which constructs a flat Cartan connection in a neighborhood of a
general minimal rational curve. In adapting this method to ${\bf X}$, we need
an intricate study of the positivity/negativity of vector bundles with respect
to a family of rational curves, which is subtler than the case of symplectic
Grassmannians because of the nature of the differential geometric structure on
${\bf X}$ arising from VMRT.
