The globular cluster ω Cen is an outstanding object in terms of both its chemical and kinematic properties. Its large mass, spread in element abundances, chemical and kinematical segregations, as well as its peculiar orbit, all suggest that it is the surviving remnant of a larger system. In this contribution we deal with the chemical evolution of ω Cen in the framework of a model where it is the remnant of a dwarf spheroidal galaxy evolved in isolation and then swallowed and partially disrupted by the Milky Way. Both infall of primordial matter and metal-enriched gas outflows are necessary in order to reproduce the observed stellar metallicity distribution function, age-metallicity relation and several abundance ratios. Yet, as long as an ordinary stellar initial mass function and standard stellar yields are adopted, we fail by far to get the enormous helium enhancement required to explain the double main sequence of ω Cen.