Lady Diana Mary Miller, 11th Countess of Mértola (born 5 July 1920) is the eldest daughter of Sackville Pelham, 5th Earl of Yarborough.
On the death of Lady Diana's father in 1948, she inherited the Portuguese countship of Mértola, while she and her sister, Lady Wendy became co-heirs to the baronies of Fauconberg and Conyers. On 15 November 1952, Lady Diana married Robert Miller (d. 1990, in an automobile accident in Harare) and they later had two daughters, Marcia Anne (born 21 June 1954) and Beatrix Diana (born 23 August 1955). In 1959, Marcia, was adopted by her aunt, Lady Wendy, and renamed Anthea Theresa. Beatrix Diana married in 1991 Simon William Jones Armstrong.
| Titles of nobility | ||
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| Preceded by Sackville Pelham |
Countess of Mértola 1948–present |
Succeeded by Incumbent |