On April 24, 2004, the red dwarf star GJ 3685A erupted the largest ultraviolet flare ever seen while NASA's Galaxy Evolution Explorer' satellite was looking its way. The flare peaked twice, pouring out in total about one million times more energy than a typical flare from our Sun. The flare lasted about 20 minutes. See this and other GALEX curiosities in the movies below.
NASA / JPL-Caltech