Depth profiling type of measurement has been performed on the Co(100 Å)/Cu(50 Å) bilayer thin film. Valence band photoemission spectra were recorded at 50 eV photon energy as a function of sputtering time. The motivation of the present work is to understand the electronic structure of the buried Co/Cu interface and the nature of intermixing in the Co and Cu layers. X-ray reflectivity and transmission electron microscopy corroborate with the photoemission results and shows a very broad intermixed Co-Cu interface. The valence band of intermixed Co/Cu interface shows the Co and Cu 3d states which are considerably shifted towards higher and lower binding energy, respectively, as compared to the bulk elemental Co and Cu 3d states. The experimental observations are explained with the help of calculations based on projected augmented wave pseudopotential method using density functional theory. The origin and the shift of feature in the valence band of the Co-Cu interface are mainly due to the formation of two different Co and Co-Cu mixed nanoclusters.