The massive star theta1 Orionis A, at the center of the famous Orion Nebula Cluster, is known as a strong variable non-thermal radio source. It is temporarily the brightest radio source in the whole Orion Nebula Cluster. The physical nature of the emission mechanism has been a matter of debate since two decades. Now, it is established that theta1 Orionis A is a close triple stellar system and that the radio emission originates
from the companion theta1 Orionis A2. I will present our analysis of available radio data in combination with NIR adaptive optics observations to investigate the radio emission mechanism and the nature of the underlying stellar source. Stringent constraints on the size of the non-thermal radio emission imply the presence of very large magnetic structures, while the infrared data suggest the stellar source is a moderately massive young late B-type star. Strong magnetic interactions between the star and its circumstellar disk seem the most plausible explanation for the non-thermal radio emission - and a solution to the long-standing enigma surrounding the OB star theta1 Orionis A.