The
B
+
c
meson is observed for the first time in heavy ion collisions. Data from the CMS detector are used to study the production of the
B
+
c
meson in lead-lead (Pb-Pb) and proton-proton (
p
p
) collisions at a center-of-mass energy per nucleon pair of
√
s
N
N
=
5.02
 
 
TeV
, via the
B
+
c
→
(
J
/
ψ
→
μ
+
μ
−
)
μ
+
ν
μ
decay. The
B
+
c
nuclear modification factor, derived from the Pb-Pb–to–
p
p
ratio of production cross sections, is measured in two bins of the trimuon transverse momentum and of the Pb-Pb collision centrality. The
B
+
c
meson is shown to be less suppressed than quarkonia and most of the open heavy-flavor mesons, suggesting that effects of the hot and dense nuclear matter created in heavy ion collisions contribute to its production. This measurement sets forth a promising new probe of the interplay of suppression and enhancement mechanisms in the production of heavy-flavor mesons in the quark-gluon plasma.