The mass is the most substantial quantities of a star. On the Main Sequence, it determines the temperature, surface gravity and the evolution or for White Dwarfs strongly correlates with the stellar radius. Currently, relations concerning stellar masses are mainly based on binary stars, where a direct measurement is possible. Since single stars evolve differently, it is important to derive the masses of single stars directly. Beside strongly model-dependent asteroseismology, astrometric microlensing is the only other usable tool to estimate single-star masses. Mass measurements with an accuracy a few percent are possible by doing precise astrometric measurements of the lensed position of a background source in combination with accurate predictions of the positions of the lensing star and the unlensed source using data of the ESA Cornerstone Mission Gaia. Further, the precise astrometric data from Gaia can be used to predict at what epochs such astrometric microlensing events will happen. I will present our analysis of the recently published eGaia DR3 catalogue for the prediction of a number of astrometric microlensing events in the near future. Especially, I will present an event to be caused by a white dwarf, which will happen in 2025, this will be a unique test case for the mass-radius relation of white dwarfs.