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The formation and evolutionary processes of galaxy bulges are still unclear, and the presence of young stars in the bulge of the Milky Way is largely debated. We recently demonstrated that Terzan 5, in the Galactic bulge, is a complex stellar system hosting stars with very different ages and a striking chemical similarity to the field population. This indicates that its progenitor was likely one of the giant structures that are thought to generate bulges through coalescence. Here we show that another globular cluster-like system in the bulge (Liller 1) hosts two distinct stellar populations with remarkably different ages: only 1-3 Gyr for the youngest, 12 Gyr for the oldest, which is impressively similar to the old component of Terzan This discovery classifies Liller 1 and Terzan 5 as sites of recent star formation in theGalactic bulge and provides clear observational proof that the hierarchical assembly of primordial massive structures contributed to the formation of the Milky Way spheroid.The picture of galaxy bulge formation is still largely debated in the literature 1 . Among the most credited scenarios, the "merging picture" proposes that galaxy bulges form from the merging of primordial substructures, either galaxies embedded in a dark matter halo 2,3 , or massive clumps generated by early disk fragmentation 4-6 . Although the vast majority of the primordial fragments should dissolve to form the bulge, it is possible that a few of them survived the total disruption, and are still present in the inner regions of the host galaxy, grossly appearing like massive globular clusters (GCs). At odds with genuine GCs, however, these fossil relics should have been massive enough to retain the iron-enriched ejecta of supernova (SN) explosions, and possibly experienced multiple bursts of star formation. As a consequence, they are expected to host multi-iron and multiage sub-populations. The first candidate fossil relic in the Galactic bulge was identified 7 back in 2009: the detailed photometric and spectroscopic study of Terzan 5 demonstrates 8-12 that this massive (~2 10 6 M ! ) stellar system hosts at least two major sub-populations, ascribable to different star formation events. The first intense and short-lived (< 1 Gyr) star formation burst occurred about 12 Gyr ago, from gas enriched by type II SNe, with sub-solar metallicity ([Fe/H]= −0.3) and enhanced [α/Fe]=+0.4 abundance ratio. The second burst occurred ~7.5 Gyr later (approximately

We used high-resolution optical HST/WFC3 and multi-conjugate adaptive optics assisted GEMINI GeMS/GSAOI observations in the near-infrared to investigate the physical properties of the globular cluster NGC 6569 in the Galactic bulge. We have obtained the deepest purely NIR color-magnitude diagram published so far for this cluster using ground-based observations, reaching K s ≈ 21.0 mag (two magnitudes below the main-sequence turn-off point). By combining the two datasets secured at two different epochs, we determined relative proper motions for a large sample of individual stars in the center of NGC 6569, allowing a robust selection of cluster member stars. Our proper motion analysis solidly demonstrates that, despite its relatively high metal content, NGC 6569 hosts some blue horizontal branch stars. A differential reddening map has been derived in the direction of the system, revealing a maximum color excess variation of about δE(B − V ) ∼ 0.12 mag in the available field of view. The absolute age of NGC 6569 has been determined for the first time. In agreement with the other few bulge globular clusters with available age estimates, NGC 6569 turns out to be old, with an age of about 12.8 Gyr, and a typical uncertainty of 0.8-1.0 Gyr.