In this talk I discuss the nature of the X-ray source 1E161348-5055, located at the centre of the supernova remnant RCW~103. Its X-ray light curve shows a period of 6.67 hr, and there is no evidence of a companion star more massive than ~0.4 solar masses. We argue that 1E161348-5055 consists of a neutron star in close orbit with a low mass main sequence star. The time signature of 6.67 hr is interpreted as the neutron star's spin period. This requires the neutron star to be endowed with a high surface magnetic field of ~10**15 G. Magnetic or/and material (propeller) torques are able to spin rapidly the young neutron star down to an asymptotic, equilibrium spin period in close synchronism with the orbital period, similarly to what happens in Polar or strongly magnetised Intermediate Polar Cataclysmic Variables. 1E161348-5055 could be the first case of a magnetar born in a young low mass binary system.