We present deep and precise multi-band photometry of the Galactic Bulge globular cluster NGC 6528 .
The current dataset includes optical and near-infrared images collected with ACS/WFC , WFC3/UVIS , and WFC3/IR on board the Hubble Space Telescope .
The images cover a time interval of almost ten years and we have been able to carry out a proper-motion separation between cluster and field stars .

We performed a detailed comparison in the m _ { F 814 W } ,m _ { F 606 W } - m _ { F 814 W } Color-Magnitude Diagram with two empirical calibrators observed in the same bands .
We found that NGC 6528 is coeval with and more metal-rich than 47 Tuc .
Moreover , it appears older and more metal-poor than the super-metal-rich open cluster NGC 6791 .
The current evidence is supported by several diagnostics ( red horizontal branch , red giant branch bump , shape of the sub-giant branch , slope of the main sequence ) that are minimally affected by uncertainties in reddening and distance .

We fit the optical observations with theoretical isochrones based on a scaled-solar chemical mixture and found an age of 11 \pm 1 Gyr and an iron abundance slightly above solar ( \hbox { [ Fe / H ] } = +0.20 ) .
The iron abundance and the old cluster age further support the recent spectroscopic findings suggesting a rapid chemical enrichment of the Galactic Bulge .