Stars comprising the Milky Way's stellar halo safeguard important chemo-dynamical information that enables the reconstruction of the mass assembly history of the Galaxy. Of particular importance are the halo populations in the innermost regions of the Milky Way, as they likely retain pivotal information that may help decode the early stages of the formation of the Galaxy, but however have so far been concealed due to the limitations in observing such regions due to high stellar density and dust extinction. In this talk I will present results from two independent studies aimed at tackling two open questions in Galactic archaeology: "What is the Milky Way's mass assembly history?"; and "How much do globular clusters (GC) contribute to the total stellar halo mass budget?". First, I will provide evidence for the discovery of a new metal-poor substructure that displays chemo-dynamic signatures of accreted populations located within the heart of the Galaxy. Given the properties of this newly identified substructure (dubbed "Heracles"), we conjecture that it is the remnant of an accretion event that occurred in the early life of the Galaxy, which constituted a major building block of the Milky Way halo, and played a major role in the formation of the Milky Way. Following, I will present results on a study focused on assessing the contribution of dissolved and/or evaporated GC stars to the Galactic stellar halo. Using a density modelling procedure, I will show results that suggest there is a much higher contribution of dissolved/evaporated GC stars in the inner regions of the Galaxy when compared to the outer regions. The results presented in this talk help shed light on the nature of Galactic stellar halo populations and the mass assembly history of the Galaxy.