On February 18, 1665, British representative Humphrey Cooke formally claimed Bombay for the British Crown in a ceremony that significantly impacted western India's future. A recently uncovered 10-page Portuguese manuscript, titled ‘Instrument of Possession’, details the transfer of the territory from the Portuguese Estado da Índia to the British, as part of a marriage treaty between King Charles II of England and Catherine of Braganza. This document, discovered by researcher Yashodhan Joshi in Lisbon, sheds light on the negotiations and conditions surrounding the transfer, emphasizing the urgency felt by Portuguese officials due to the rising power of Chhatrapati Shivaji Maharaj. The manuscript not only records the formalities of the transfer but also highlights Bombay's transition from a fragmented collection of fishing villages to a unified strategic territory. It details the conditions imposed by the Portuguese, ensuring continued access to the harbor and protections for local Catholic residents. The document also reveals discrepancies in historical records regarding the transfer date, with Portuguese sources citing February 18, while British records refer to February 8. This discovery provides valuable context for understanding the political landscape of the time and the factors influencing colonial decisions. Within three years, in 1668, the British Crown leased Bombay to the East India Company, paving the way for its evolution into a crucial commercial hub in colonial India.