ITV News' Rohit Kachroo speaks to Shamima Begum in Syria
Shamima Begum, who is now 19, was found in a refugee camp in Syria last week, gave birth to a baby boy at the weekend, and wants to return to the UK.
International law forbids nations from making people stateless by revoking their only citizenship, but it is possible Ms Begum, who is of Bangladeshi heritage, held dual citizenship.
How can Shamima be stripped of her citizenship?
A 2017 government report on the issue said the Home Secretary has the power to "deprive a person of British citizenship" if it would be "conducive to the public good".
However, this only applies if the person would not be left stateless. If it is the case Ms Begum is a dual national, she could have her British citizenship stripped.
But Ms Begum does not hold a Bangladeshi passport and has never lived there.
Barrister David Anderson QC, who previously served as a reviewer of terrorism legislation, told the Press Association: "Those born as British citizens who are not dual nationals cannot be stripped of their citizenship in any circumstances."
What has the Home Office said?
The Home Office said such decisions are "not taken lightly" and are carried out "in order to protect this country".
"We do not comment on individual cases, but any decisions to deprive individuals of their citizenship are based on all available evidence and not taken lightly."
"Please find enclosed papers that relate to a decision taken by the Home Secretary, to deprive your daughter, Shamima Begum, of her British citizenship," it read.
How has Shamima Begum reacted to the news?
"I'm a bit shocked. It's a bit unjust on me and my son," the IS bride said as ITV News Security Editor Rohit Kachroo handed her the letter.
The 19-year-old Ms Begum, who gave birth to her baby boy on Sunday, said she had not been informed of the decision as she received the letter.
"I don't know what to say," she said. "I am not that shocked but I am a bit shocked. It’s a bit upsetting and frustrating. I feel like it’s a bit unjust on me and my son."
Can Ms Begum appeal the Home Office's decision to revoke her British citizenship?
According to the letter, Ms Begum has the right to appeal the decision to the Special Immigration Appeals Commission (SIAC).
The SIAC is independent of the Government and allows individuals to appeal against immigration decisions by the Home Office, such as deportations and the removal of citizenship.
Those who are outside of the UK have 28 days to lodge an appeal from the time they receive their Home Office letter.
Number of people deprived of British citizenship in 2017
Is revoking Shamima Begum's citizenship legal?
Amendments were made to British national laws in 2014 which made it easier to strip dual nationals of their British citizenship.
These measures were primarily aimed at terrorists who could potentially undermine UK security, for example those who fled to Syria to fight and were attempting to return home.
There are two other instances when British citizenship can be removed, which are permissible even if the person would be rendered stateless.
Deprivation of citizenship can be made if a person obtained their citizenship through registration or naturalisation and the Home Secretary is "satisfied that this was obtained by fraud, false representation or the concealment of a material fact".
Secondly, when citizenship is obtained through naturalisation and the Home Secretary believes removing it would be "conducive to the public good" because the person acted in way which is "seriously prejudicial to the vital interests of United Kingdom, any of the Islands, or any British overseas territory".
However, this power, introduced in the Immigration Act 2014, can only be used if there are reasonable grounds for believing the person is able to acquire citizenship of another country, thereby avoiding remaining stateless.
Figures for 2017 show that 104 people were deprived of their British citizenship - up from 14 in the previous year.