The Queen expressed her "sincere wish" for Camilla to be given that title in a statement commemorating her reign's 70th anniversary.
The Queen is the first British monarch to reach the Platinum Jubilee milestone. She'll be spending her day alone on the Sandringham estate, ahead of the national celebrations in June.
Following the death of her father, George VI, on February 6, 1952, the Queen's reign started when she was 25 years old. The monarch said she recalls the day "as much for the death of my father, King George VI, as for the start of my reign" 70 years later.
"I would want to convey my gratitude to you all for your support," the 95-year-old said in a written statement to the country. "I remain eternally thankful for, and humbled by, the dedication and affection that you continue to show me."
The monarch's first Jubilee without the Duke of Edinburgh, her 73-year-old husband, who died last year.