Once referred to as 'simple stellar populations', globular clusters (GCs) are not simple at all, in that they display significant and peculiar star-to-star abundance variations. These are most likely the records of a complex star formation history. This picture is supported by the presence of multiple main sequences (MSs) in two massive Galactic GCs, Omega Cen and NGC2808. The bluer MSs are - surprisingly - more metal-rich than the red ones, or have the same iron content. This, at present, can be understood only in terms of an extreme helium enhancement in the blue population. To study the possible origin of the huge helium enrichment attributed to the stars on the blue MS of Omega Cen, we make use of a chemical evolution model that has proven able to reproduce other major observed properties of the cluster, namely its stellar metallicity distribution function, age-metallicity relation and trends of several abundance ratios with metallicity. In this framework, the key condition to satisfy all the available observational constraints is that a galactic-scale outflow develops in a much more massive parent system, as a consequence of multiple supernova explosions in a shallow potential well. This galactic wind must carry out preferentially the metals produced by explosive nucleosynthesis in supernovae, whereas elements restored to the interstellar medium through low-energy stellar winds by both asymptotic giant branch (AGB) and massive stars must be mostly retained within the proto-cluster potential well. Assuming that helium is ejected through slow winds by both AGB stars and fast-rotating massive stars, the interstellar medium of Omega Cen's parent galaxy gets naturally enriched in helium in the course of its evolution.