@piotto2012], and multimodal red-giant branches (RGBs) and SGBs in the $I$ vs.$U-I$ or $V$ vs.$U-V$ CMDs, with metal-rich stars populating red RGBs and faint SGBs [e.g. @marino2011; @lee2015; @lee2020].

Based on multi-band photometry of 58 GCs, @milone2017 find that Type II GCs make up 17% of the studied clusters. The fact that Type II clusters exhibit star-to-star metallicity variation, suggests that they have been able to retain a small amount of the material ejected by supernovae. In this respect, they differ from Type I GCs, where supernova yields seem to have no effect on the chemical composition of second-population stars.

Due to their large total masses and the complexity of their stellar populations, it has been suggested that Type II GCs formed in the environment of dwarf galaxies, e.g. in their nucleus.

These galaxies are then tidally destroyed by the interaction with the Milky Way. This possibility is supported by the observation that the Type II GC M54 lies in the nucleus of the Sagittarius dwarf galaxy [@bellazzini2008] and by the fact that the class of Type II GC includes NGC5139 ($\omega\,$Centauri), which is often considered the remnant of a dwarf [e.g. @bekki2003]. Moreover, based on the integrals of motion 