  Spatially periodic structures with a long range period, referred to as
moir\'e pattern, can be obtained in van der Waals bilayers in the presence of a
small stacking angle or of lattice mismatch between the monolayers. Theoretical
predictions suggest that the resulting spatially periodic variation of the band
structure modifies the optical properties of both intra and interlayer excitons
of transition metal dichalcogenides heterostructures. Here, we report on the
impact of the moir\'e pattern formed in a MoSe$_2$/MoS$_2$ heterobilayer
encapsulated in hexagonal boron nitride. The periodic in-plane potential
results in a splitting of the MoSe$_2$ exciton and trion in both emission and
absorption spectra. The observed energy difference between the split peaks is
fully consistent with theoretical predictions.
