Britain's ITV News has obtained a copy of the letter from the UK Home Office to Begum's mother served yesterday, along with papers formally revoking her citizenship and appeal material.
Islamic State schoolgirl Shamima Begum has had her British citizenship revoked, her family has been told in a letter from the Home Office.
The letter, obtained by ITV News, was received by Ms Begum's mother on Tuesday.
"Please find enclosed papers that relate to a decision taken by the Home Secretary, to deprive your daughter, Shamima Begum, of her British citizenship," the letter read.
"In light of the circumstances of your daughter, the notice of the Home Secretary's decision has been served of file today (19th February), and the order removing her British citizenship has subsequently been made."
The letter went on to urge Ms Begum's family to make her aware of the decision, and added that she had a right to appeal.
In a statement posted on Twitter, the family's lawyer, Tasnime Akunjee, said: "Family are very disappointed with the Home Office's intention to have an order made depriving Shamima of her citizenship.
"We are considering all legal avenues to challenge this decision."