As per case facts, the Petitioner applied for a medical fellowship with a two-stage selection process, Stage-II being a 'departmental clinical/practical/lab based assessment' as per the Prospectus. After qualifying Stage-I, ... an online CV and presentation-based interview was conducted for Stage-II, differing from the Prospectus. The Petitioner participated, failed to secure the seat, and challenged this deviation. The question arose whether the Respondents’ alteration of the Stage-II assessment method violated the Prospectus and if the Petitioner was estopped from challenging it after participation. Finally, the Court ruled that the online interview was a clear deviation from the Prospectus. It held that the estoppel principle does not apply when challenging such fundamental illegality, allowing the Petitioner to challenge despite participation. Consequently, the Stage-II result was cancelled, and a re-assessment as per the Prospectus was directed.