On the K-stability of blow-ups of projective bundles

We investigate the K-stability of certain blow-ups of ${\mathbb{P}}^1$-bundles over a Fano variety $V$, where the ${\mathbb{P}}^1$-bundle is the projective compactification of a line bundle $L$ proportional to $-K_V$ and the center of the blow-up is the image along a positive section of a divisor $B$ also proportional to $L$. When $V$ and $B$ are smooth, we show that, for $B{\sim }_{\mathbb{Q}}2L$, the K-semistability and K-polystability of the blow-up is equivalent to the K-semistability and K-polystability of the log Fano pair $(V,aB)$ for some coefficient $a$ explicitly computed. We also show that, for $B{\sim }_{\mathbb{Q}}lL$, $l\mathrm{\ne }2$, the blow-up is K-unstable.