Part of an eclipsing binary, white dwarf star WD 1202-024 is eclipsed by its partner (a brown dwarf) once every 71 minutes at a speed of well over 100 kilometres per second. This is an incredibly short orbital period, and has some fascinating implications.
In particular, this suggests that about 50 million years ago, when the white dwarf was in its previous red giant phase (in which a main sequence star massively expands in volume after burning through all usable hydrogen), it would have encompassed the brown dwarf companion entirely.
Data suggests the brown dwarf - weighing in at around 70 jovian masses and thus too small for fusion on its own - would have maintained its integrity during this period (the density of the outer layers of a red giant is extremely low) and is not yet a cataclysmic variable. Therefore, we can conclude that until the outer envelope was blown off it would have been orbiting inside its companion star.
Scott Manley gives a fascinating rundown of this and gives a few examples of other stars exhibiting behaviour that is consistent with multiple cores orbiting within a single stellar envelope.
A recent discovery identified a brown dwarf orbiting a young white dwarf, suggesting that millions of years ago the brown dwarf was orbiting *inside* the primary star. As it turns out, this is not the first time astronomers have invoked the concept of one star inside another.