Background: The study examines alloparental care and adoption in the Sri Lankan leopard population at Yala National Park, Sri Lanka. Using the Multi Point Leopard Identification Method, it documents a remarkable instance: a leopard cub [YM 67] initially adopted by its maternal aunt [YF 46], and later by another female [YF 15] with no prior connection to the cub. We consider this behaviour is noteworthy in especially solitary animal species such as leopards. Methods: Our study was conducted for a period of two years and five months (from February 2021 to July 2023). Our observations highlight the dynamics of these adoptions and the behaviours exhibited. Altruistic acts, such as feeding, brushing, and shielding the cubs, were observed. These inspections challenge the conventional knowledge regarding leopard behaviours. Notably, YF 15’s adoption of YM 67, despite their lack of genetic relatedness, exemplifies a form of mutually beneficial reciprocal altruism, benefiting both parties. Discussion: The following study explains leopard adoptions using evolutionary theories like kin altruism and reciprocal altruism. It suggests factors such as genetic relatedness, mutual dependency, and possible misidentification influenced the act of adoption. These rare altruistic acts benefit the leopard population. Conclusion: Our study opposes traditional concepts of solitary Sri Lankan leopards. Altruistic behaviours, influenced by genetic relatedness and reciprocal benefits, emphasize social dynamics in predator populations. These findings enhance the understanding of evolutionary mechanisms and cooperative behaviours in maintaining population fitness in the Sri Lankan leopard population.