This paper describes an experimental study of the evolution of spray structure in an internally mixed, twin-fluid swirl atomizer. The atomization in such atomizers is perceived to be strongly influenced by the mass flow ratio of the atomizing gas and the liquid The order of magnitude of the ALR (air-liquid mass flow ratio), for which the study was made, ranged from 0.001 to 0.1. A laser sheet visualization technique was used to study the primary spray formation process. It was observed that at low ALR a fully developed air core inside the hollow conical spray is present, suggesting the assistance provided by the atomizing air to the atomization process by destabilizing the liquid internally. At high ALR conditions of around 0.1, a solid-cone spray shape is observed. At moderate ALRs, a mixed cone is formed, having an outer hollow structure and a solid core, with a gap between the inner and outer cone. This can be attributed to the combined effect of swirl that produces the hollow cone and the increase in the axial momentum of the liquid inside the atomizer due to squeezing by the surrounding atomizing air, which forms the inner core. Also, the phenomenon of liquid disintegration in terms of breaking length and the droplet diameter for different ALR conditions were analyzed in this study. It was observed that the structure of the spray, e.g., cone angle, solidity, and breaking length, do not change much with the increase in ALR beyond a critical value of 0.08. The variation from hollow to solid cones demonstrated by the atomizer in this study makes it flexible enough to be used for various commercial applications, since the atomizer is capable of providing a wide range of spray patterns depending on the application requirement.