We report the formation of a new structurally complex intermetallic phase in the Ce-Au-Sn system. This phase has been observed in an ingot with nominal composition Ce16.7Au72.2Sn11.1. In addition, we have identified by transmission electron microscopy operating in two-beam conditions the occurrence of planar defects, characterized as grains boundaries located between the cubic 1/1 CeAuSn approximant and the new phase. Tilt series of electron diffraction patterns of this new structure have been recorded along two main directions. These measurements have been used for the reconstruction of the reciprocal space. The resulting cell is hexagonal, with ah ≈ 1.53 nm and ch ≈ 1.52 nm. It is structurally related to the Gd13Cd58 structure type (P63/mmc), where some Cd atoms are icosahedrally coordinated. The orientation relationships between the two complex structures across planar boundaries have been deduced from the lattice fringes transmission electron microscopy images.