Hot subdwarf B stars ( sdBs ) are extreme horizontal branch stars believed to originate from close binary evolution .
Indeed about half of the known sdB stars are found in close binaries with periods ranging from a few hours to a few days .
The enormous mass loss required to remove the hydrogen envelope of the red-giant progenitor almost entirely can be explained by common envelope ejection .
A rare subclass of these binaries are the eclipsing HW Vir binaries where the sdB is orbited by a dwarf M star .
Here we report the discovery of an HW Vir system in the course of the MUCHFUSS project .
A most likely substellar object ( \simeq 0.068 M _ { \odot } ) was found to orbit the hot subdwarf J08205+0008 with a period of 0.096 days .
Since the eclipses are total , the system parameters are very well constrained .
J08205+0008 has the lowest unambiguously measured companion mass yet found in a subdwarf B binary .
This implies that the most likely substellar companion has not only survived the engulfment by the red-giant envelope , but also triggered its ejection and enabled the sdB star to form .
The system provides evidence that brown dwarfs may indeed be able to significantly affect late stellar evolution .