In the last few years, several giant-amplitude, non-recurrent X-ray flares have been observed from optically non-active galaxies. The observations were interpreted in terms of the long-predicted tidal disruption flares of stars captured by supermassive black holes. In this contribution, we review the observations and interpretation of the X-ray flares and add some new thoughts. Future X-ray observations of the flare events are expected to open up a new window to detect and investigate SMBHs and their immediate environment in galaxies. Here, we concentrate on the possibility to detect new X-ray flares in deep fields with the planned European X-ray mission XEUS.