  We study $B_c$ production in high-energy nuclear collisions in a transport
approach with dissociation and regeneration at finite temperatures. Due to the
rare production in p+p collisions and the strong combination of uncorrelated
$c$ and $\bar b$ quarks in the quark-gluon plasma, the $B_c$ yield is clearly
enhanced in the nuclear collisions at the Large Hadron Collider. Besides, the
centrality and momentum-dependent yield of $B_c$ sensitively reflect the
thermalization degree of bottom quarks. And the newly observed experimental
data favors a far from the thermal bottom quark distribution in the quark-gluon
plasma.
