A letter written in Persian by Lakshmibai, Rani of Jhansi, to the then governor-general of the East India Company Lord Dalhousie has been discovered in the British Library.
The letter found in the archives of the library was written shortly before the start of India's first war of independence in 1857.
"This a letter written by an iconic talisman for the nationalist narrative in India. The letter is part of a collection of documents known as the Bowring Collection," Deepika Ahlawat, research curator for the Victoria and Albert Museum's Maharaja exhibition currently being staged in London told BBC.
"The collection is named after Lewin Bentham Bowring, a civil servant working in India who gathered a remarkable collection of documents, photographs and ephemera relating to the maharajas," she said.
In the letter, the Rani of Jhansi describes the fateful events on the night her husband died.
Ahlawat said: "But under the doctrine of lapse then being imposed by the EIC, any Indian kingdom whose ruler died without an heir, or who was guilty of misrule - was subsumed into Company territory".
Lakshmibai wrote that her husband adopted a suitable heir before his death by performing all the necessary rites for her adopted son, Damodar Rao, to be accepted as the next Raja of Jhansi.
But Lord Dalhousie did not recognise the adoption and threatened to annex Jhansi. In 1857 the Rani joined the rebellion against the British and personally led her troops in battle.