With close ties to Britain’s royal family, Ms. Knatchbull — also known as Lady Patricia — belonged to what an official biography called “a dynasty of royal, political and wealthy relations.” She was born without a formal title, the elder daughter of Lord Louis Mountbatten, Britain’s onetime First Sea Lord and its last imperial viceroy in India, and a prominent heiress of the day, Edwina Ashley. Through her marriage in 1946 to the moviemaker John Knatchbull, the seventh Baron Brabourne, she became Lady Brabourne. She inherited the title Countess Mountbatten of Burma after the mayhem on Aug. 27, 1979, when the family fishing boat, the Shadow V, was bombed by the Irish Republican Army off the coast of Ireland. Timothy Knatchbull’s 14-year-old identical twin, Nicholas one of Ms. Knatchbull’s seven children, was killed, as was their grandfather, Lord Mountbatten, 79, and a boat hand, Paul Maxwell, 15. Ms. Knatchbull’s mother-in-law, the Dowager Baroness Doreen Brabourne, 83, died in a hospital the next day. Patricia Edwina Victoria Mountbatten was born in London on Feb. 14, 1924. In the family tree, she ranked as third cousin to Queen Elizabeth II and first cousin to Prince Philip, who married Elizabeth in 1947. She and her sister were both great-great-grandchildren of Queen Victoria. On her father’s side, the family was descended from German aristocracy. The name Battenberg was changed to Mountbatten during World War I, when anti-German sentiment ran strong. They belonged to a social circle that inhabited vast mansions and included Queen Mary, King Edward VIII and Wallis Simpson, the American socialite for whom he abdicated the British throne. With the outbreak of World War II, she and her sister Pamela were evacuated from Britain in 1940 and sent to New York to live with the socialite Grace Vanderbilt, the wife of Cornelius Vanderbilt III, at their palatial apartment on Fifth Ave. She married John Knatchbull, a former aide to her father who went on to produce movies, including “A Passage to India,” “Murder on the Orient Express” and “Death on the Nile.” He died at 80 in 2005. Ms. Knatchbull is survived by six children; her sister, Pamela; and 18 grandchildren. Her oldest son, Norton, has inherited the title Earl Mountbatten of Burma.