In conventional monopulse radar, the bearing of a single target within the mainlobe of the transmitted beam is estimated via a ML procedure based in a 2-D beamspace defined by sum and difference beams. For the case of two closely spaced targets angularly located within the mainlobe of the transmitted beam, 3D-BDML is a computationally simple ML bearing estimation scheme which operates in a 3-D beamspace generated by three orthogonal, classical beamformers. The presence of strong interferers angularly located outside the mainlobe encompassing the two targets of interest necessitates the use of adaptively formed left, center, and right beams. Let M denote the number of elements comprising the array. Novel procedures are developed for the construction of an M x 3 interference cancellation matrix beamformer which retains those properties of the M x 3 classical matrix beamformer critical to the computational simplicity of 3D-BDML. The most important of these is commonality of M - 3 nulls among the left, center, and right beams. Simulations are presented demonstrating the excellent performance of both single frequency and multifrequency 3D-BDML incorporating interference cancellation in a simulated low-angle radar tracking environment.