The Duke and Duchess of Cambridge's first child, whether a boy or a girl, will become heir to the throne after 15 other Commonwealth nations gave their consent to the change which initially favoured men, ministers have confirmed.
The government reached an agreement this week with all other Commonwealth countries to press ahead with a bill ending discrimination against women in the succession to the British throne.
Deputy Prime Minister Nick Clegg said the government would now introduce the Succession to the Crown Bill in the House of Commons as soon as possible.
He also revealed that by "wonderful coincidence" the final formal consents from other Commonwealth realms were received just as the Duke and Duchess revealed that they are expecting their first child.
Nick Clegg described the realms' consent as "a historic moment for our country and our monarchy."
He said: "We can also all celebrate that whether the baby is a boy or a girl, they will have an equal claim to the throne. It's a wonderful coincidence that the final confirmation from the other realms arrived on the very day that the Duke and Duchess of Cambridge made their announcement.
"The government will soon introduce the Succession to the Crown Bill which will make our old fashioned rules fit for the 21st Century. It will write down in law what we agreed back in 2011 – that if the Duke and Duchess Cambridge have a baby girl, she can one day be our Queen even if she later has younger brothers."
In October last year at the Commonwealth Heads of Government Meeting all 16 nations - of which the Queen is head of state - voted for constitutional changes, bringing equality to the laws of succession.
The monarch seemed to signify her approval at the time when she made a speech about the theme of the conference, Women as Agents of Change.
The pregnant duchess is in hospital but is feeling much better, royal officials said on Tuesday.
Kate is spending her third day being treated for acute morning sickness in the King Edward VII Hospital in central London.
A St James's Palace spokesman said: "The Duchess of Cambridge is continuing to feel better. She and the Duke are immensely grateful for the good wishes they have received. She will remain in hospital at present."
Her husband Prince William has been by her side since Monday. He was photographed leaving the hospital on Tuesday night with a smile on his face, indicating that Kate is in much better spirits.
HELLO! WILL RELEASE A SPECIAL EDITION WITH ALL THE DETAILS ON THE COUPLE'S JOYFUL NEWS AS CONGRATULATIONS POUR IN FROM AROUND THE WORLD. PLUS: THE LATEST ON KATE'S SICKNESS SCARE AND THE TELLTALE SIGNS THAT SHE WAS EXPECTING.
DON'T MISS YOUR SOUVENIR COPY OF HELLO!, ON SALE FROM WEDNESDAY.
Watch: Prince William takes George to meet his sister
It's a little princess!