Carrie Symonds will go with Britain's Prime Minister Boris Johnson when he stays with the Queen at Balmoral later this northern summer.
The prime minister's girlfriend, 31, will attend the traditional weekend at the monarch's Scottish estate, sources told the PA news agency.
Every year the Queen spends the summer at Balmoral Castle in Scotland where she is joined by other members of the royal family - and traditionally hosts the prime minister for a weekend in September.
Symonds will be the first unmarried partner of a sitting PM to stay at Balmoral.
Symonds, who last week gave a speech on protecting the environment, may find herself at odds with the royals, whose pastimes famously include blood sports.
The public relations expert, who lives in Downing Street with Johnson, 55, resigned as director of communications for the Conservatives last year and is now a senior adviser at Oceana, a US-based environmental campaign group.
Australian Associated Press