Twinning, in-addition to dislocation slip, is a prevalent deformation mechanism in low-symmetry (hexagonal close packed - hcp) metals. Deformation twins are shear transformed domains which evolve in three sequential stages: twin nucleation, twin propagation and twin growth. Most of the work carried out on hcp twins has been limited to static and two-dimensional studies. On the contrary, the short- and medium- range interactions among numerous transformed domains in the crystal and their connection to the kinetics of growth of individual domains can only be understood via three-dimensional analysis. In the present work, the newly developed DDD-FFT technique is used to model the three-dimensional nature of twins and study the influence of interfacial defects on twin growth in magnesium single crystal. The stress state in the vicinity of the twin is extracted for an experimentally observed (01-12) [0-111] tensile twin with a shear eigenstrain ~13%. Plastic relaxation around the twin was observed to change the stress state in the vicinity of the twin. Studying the role of surface energy and local stress fields for different transformed domains provides insight into the dynamics of interfacial defects and their connection to twin growth. Dislocation-twin interactions were observed to not only influence local stresses but also twin growth and, in-turn, the overall mechanical response of the magnesium crystal.