  We holographically compute the R\'enyi relative divergence $D_{\alpha}
(\rho_{+} || \rho_{-})$ between two density matrices $\rho_{+}, \; \rho_{-}$
prepared by path integrals with constant background fields $\lambda_{\pm}$
coupled to a marginal operator in JT gravity. Our calculation is non
perturbative in the difference between two sources $ \lambda_{+} -\lambda_{-}$.
When this difference is large, the bulk geometry becomes a black hole with the
maximal temperature allowed by the R\'enyi index $\alpha$. In this limit, we
find an analytic expression of the R\'enyi relative divergence, which is given
by the on shell action of the back reacted black hole plus the contribution
coming from the discontinuous change of the background field.
