Combined high-resolution ARPES with STM measurements are presented to investigate the Ag/Cu(111) interface. In the submonolayer range, the irreversible moiré to triangular structural transformation is revealed by the change of the surface state energy. A transient state, seen in our ARPES measurements, is connected to a nanoscopic pre-formed triangular area evidenced by STM. In addition, a careful analysis of the annealing effect on a 1.6 monolayer film suggests that the presence of the second layer limits the entrance of vacancies in the topmost Cu layer and prevents the formation of the triangular dislocation loop pattern. These results emphasize how to use surface states as a sensitive probe of surface and interface reconstructions from their spectroscopic signature.