Binary stellar systems are common in our local Universe: their fractions is about 50% or more. The interaction between the binary components give raise to an exciting zoo of astronomical phenomena, such as cataclysmic variables, X-ray binaries, pulsars, stripped-envelope supernova or coalescence of stellar-mass black holes, as recently shown by LIGO. One particularly mysterious transitory phase of binary evolution is the common envelope (CE) phase, when both stars expand enough to create a common gas system with its companion. In my talk, I will present the observations of an unusual red transient in galaxy Messier 101. Its observational signature reveals that it was likely an ejection of the CE in a massive binary system.