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Mary Scott, 3rd Countess of Buccleuch and Countess of Tarras (August 31, 1647–March 11, 1661) was a young Scottish peeress, the daughter of Francis Scott, 2nd Earl of Buccleuch. Mary succeeded to her father's titles aged 4, when he died in 1651. She immediately became one of the most desirable matches of the kingdom. On February 9, 1659, she married Walter Scott of Highchester (herself only 11 years old at the time and her husband, 14), who was created Earl of Tarras a year later. Her mother arranged the marriage without proclamation, with a warrant from the presbytery of Kirkcaldy. It created a lot of noise at the time and the court ruled that Mary should be separated from her husband until she was 12 years of age. During their separation they continued a very affectionate correspondence. However, she fell ill and died two years after their reunion, aged 13 in 1661 and her titles passed to her sister, Anne.