The Queen has given her formal consent to the marriage of Prince Harry and Meghan Markle.
In a letter to the Privy Council, the monarch expressed her approval of the upcoming wedding between her "most dearly beloved grandson" and his fiancee, 36.
A similar letter was signed by Her Majesty just one week before the 2011 wedding of Prince William and Kate Middleton.
At a Privy Council meeting on Wednesday, the monarch made the declaration and will have signed a Great Seal of the Realm.
It read: "I declare My Consent to a Contract of Matrimony between My Most Dearly Beloved Grandson Prince Henry Charles Albert David of Wales and Rachel Meghan Markle, which Consent I am causing to be signified under the Great Seal and to be entered in the Books of the Privy Council."
The first six people in the line of succession must have the Queen's consent before they can marry, as set out by the Succession to the Crown Act 2013.
Should Prince Harry have married Meghan without the monarch's approval, he and his descendants would be banned from ever ascending to the throne.
The act's introduction saw sex removed as a determining factor in the line of succession, meaning Prince Harry is fifth-in-line behind Princess Charlotte.
A monarch's permission has been sought for those in the line of succession since the 18th century.
Under the Royal Marriages Act 1772, all descendants of George II had to obtain the sovereign's agreement before they wed, otherwise the marriage was invalid.
A Buckingham Palace spokesman said: "Her Majesty finally gave consent to the marriage of Prince Harry and Ms Meghan Markle under the Succession to the Crown Act by making a declaration at the meeting of the Privy Council on March 14, 2018."
The announcement comes as it was revealed Prince Harry took Meghan Markle to a secret meeting with traumatised war veterans that he says "shocked us to our core".
The 33-year-old – who himself served two tours on the frontline in Afghanistan - told how over the years he has seen his own forces buddies "suffer, struggling to seek out the help they desperately need".
A few weeks ago he took Meghan, 36, to meet other former service men and women trying to get care for crippling mental health problems, as he was keen to introduce her to a side of his public work that held such enormous personal resonance.
The pair visited Colchester Garrison, in Essex, where they spent time at The North Essex Veterans Mental Health Network away from the cameras and glare of publicity.
The former actress, who will become his wife on May 19 at Windsor Castle, has herself been holding private meetings with charities as she prepares to carve out her own role in 'The Firm'.
Harry said: "Some of the stories Meghan and I heard when we visited Colchester Garrison a few weeks ago shocked us to our core."
His comments, made in a keynote speech at the Veterans Mental Health Conference at Kings College London, came as he insisted "military service is enriching and good for society".
Harry first served in Afghanistan as a forward air controller while serving in the Blues and Royals.
During his second tour, he later admitted to killing a Taliban commander as the co-pilot gunner on a fearsome Apache helicopter.
But the prince said one of the most troubling aspects of his experience in the military was watching his brothers in arms see their mental health deteriorate and struggle to find help.
The groom-to-be said: "For me, this issue is personal. My time in the Army gave me the strongest respect for everyone who wears the uniform.
"It is a community I am proud to belong to, and I will always seek out anyway that I can to support it.
"I have seen those I have served with suffer, struggling to seek out the help they desperately need.
"And we know there are more just like them who continue to suffer in silence.
"And when the individual doesn't or can't reach out for help, it is also their families who suffer; especially their spouses and children, who are left feeling desperate and confused as they try to seek appropriate help for the ones they love."
The project Harry and Meghan went to see in Essex is designed to give veterans all the help they need in one place.
It is part of a partnership called TILS, the Transition, Intervention and Liaison Services, which brings various health bodies together under one roof.
The intention is to create a 'one stop shop' - so that service men and women get the full help available without getting lost in the system.
Harry said: "Meghan and I recently visited The North Essex Veterans Mental Health Network and we got to see the amazing work they are doing in Colchester.
"They have produced a seamless journey for veterans, with centrally held case management that results in transitional, not transactional movement across care services.
"This style of service has been adopted by NHS England and is now in operation across a number of health trusts across the country."
He added: "Our experiences show that employers value veterans and we want to push that message that they are incredible assets to any business.
"Any employer would be lucky to have them as part of your team – and that's a fact.
"Serving your country makes you a better person for your family, community and country; increased confidence, discipline, teamwork, loyalty, and the ability to realise huge potential in yourself."