We discuss the recent detection of a strong , organized magnetic field in the bright , broad-line B2V star , HR 5907 , using the ESPaDOnS spectropolarimeter on the CFHT as part of the Magnetism in Massive Stars ( MiMeS ) survey . We find a rotational period of 0.50833 days , making it the fastest-rotating , non-degenerate magnetic star ever detected . Like the previous rapid-rotation record holder HR 7355 ( also discovered by MiMeS : Oksala et al . 2010 , Rivinius et al . 2010 ) , this star shows emission line variability that is diagnostic of a structured magnetosphere . Key words : techniques : spectroscopic , stars : magnetic fields , stars : individual ( HR 5907 )