The stability of all fullerenes (closed carbon cages composed of pentagons and hexagons) can be explained by a simple empirical rule that forbids direct pentagon pentagon junctions (the isolated pentagon rule). Among thousands of possible fullerene structures, only one was predicted to violate this rule, namely, C-2v-symmetric C-#11188(72). In this work, we present the synthesis and isolation of this elusive fullerene cage for the first time. The C-2v-C-72 cage was captured by in situ chlorination to form C72Cl4, whose structure was unambiguously determined by single-crystal X-ray analysis. The chlorination pattern and resulting stability of C72Cl4 are discussed.