MPs have called for changes to the rules of succession
The fiancee of the Queen's grandson has given up her Catholic faith - a move that allows her partner Peter Phillips to retain his right to the throne.
Autumn Kelly has joined the Church of England, Buckingham Palace said.
If she had not changed churches, her future husband, who is 11th in line to the throne, would have had to give up his right to succession to the throne.
Since 1701 heirs to the throne marrying Catholics cannot become sovereigns. The couple are due to marry on 17 May.
A Buckingham Palace spokeswoman confirmed the conversion had taken place and said: "She was welcomed into the Church of England some time ago."
The conversion, which has no formal procedure, may just have involved Miss Kelly being welcomed into a new church.
The decision follows calls by MPs to use equality legislation to abolish a 300-year-old law which gives males precedence in the royal line of succession.
Solicitor General Vera Baird also said she wanted to repeal the law forcing royals marrying Catholics to renounce their place in the line of succession.
A Ministry of Justice spokeswoman said: "The government has always stood firmly against discrimination in all its forms, including against Roman Catholics, and we will continue to do so.
"To bring about changes to the law on succession would be a complex undertaking involving amendment or repeal of a number of items of related legislation, as well as requiring the consent of legislatures of member nations of the Commonwealth."
The spokeswoman said they were "of course ready to consider the arguments" but that there are no immediate plans to legislate on the issue.