See Margaret Cavendish, Duchess of Newcastle-upon-Tyne for the poet and writer (born Margaret Lucas).

Margaret Cavendish (22 October 1661 – 24 December 1716, London) was the second child of Henry Cavendish, 2nd Duke of Newcastle-upon-Tyne and his wife Frances Pierrepoint.

On 1 March 1690 she married John Holles, 1st Duke of Newcastle-upon-Tyne (of the second creation in 1694, the first creation having become extinct in 1691). They had one child, Lady Henrietta Cavendish Holles

Henrietta Harley, Countess of Oxford and Mortimer

Henrietta Harley , Countess of Oxford and Countess Mortimer was an English noblewoman, the only child and heiress of John Holles, 1st Duke of Newcastle and his wife, the former Lady Margaret Cavendish, daughter of Henry Cavendish, 2nd Duke of Newcastle-upon-Tyne.Her hand was sought in marriage...

 (1694–1755), who married the 2nd Earl of Oxford and Mortimer

Edward Harley, 2nd Earl of Oxford and Earl Mortimer

Edward Harley, 2nd Earl of Oxford and Earl Mortimer , styled Lord Harley between 1711 and 1724, was a British politician, bibliophile, collector and patron of the arts.-Background:...

 and was mother to Margaret Bentinck, Duchess of Portland

Margaret Bentinck, Duchess of Portland

Margaret Cavendish Bentinck, Duchess of Portland , styled Lady Margaret Harley before 1734, Duchess of Portland from 1734 to her husband's death in 1761, and Dowager Duchess of Portland from 1761 until her own death in 1785...

.