Cecily was the aunt of Richard Neville, 16th Earl of Warwick, one of the leading peers and military commanders of his generation, a great-aunt of queen consort Anne Neville, who married her son Richard III, and a great-great-great-aunt of queen consort Catherine Parr, sixth wife of her great-grandson, King Henry VIII.

Their next son, the future King Edward IV, was born in Rouen on 28 April 1442 and immediately baptised privately in a small side chapel.

He would later be accused of illegitimacy by his cousin, Richard Neville, 16th Earl of Warwick, and by his own brother, George, Duke of Clarence, a common method of discrediting political enemies.

Nonetheless, some modern historians give serious consideration to the question, and use Edward's date of birth as supporting evidence: assuming Edward was not premature (there being no evidence either way), Richard of York would have been several days' march from Cecily at the time of conception and the baby's baptism was a simple and private affair, unlike that of his younger brother Edmund, Earl of Rutland, which was public and lavish.

Around 1454, when Richard began to resent the influence of Edmund Beaufort, 2nd Duke of Somerset (a first cousin of his wife), Cecily spoke with queen consort Margaret of Anjou on his behalf.

When a parliament began to debate the fate of the Duke of York and his supporters in November 1459, Cecily travelled to London to plead for her husband.

When Cecily moved to Baynard's Castle in London, it became the Yorkist headquarters, and after Edward defeated the Lancastrians at the Battle of Towton and ascended the throne, she was honoured as the mother of the king.

Edward IV was briefly overthrown by Warwick and Margaret of Anjou, and for about six months (October 1470 – April 1471), Henry VI was restored to the throne.

Duchess Cecily was on good terms with Richard's wife Lady Anne Neville (her grandniece in addition to being her daughter-in-law), with whom she discussed religious works such as the writings of Mechtilde of Hackeborn.

On 18 January 1486, Cecily's granddaughter, Elizabeth of York, eldest daughter of Edward IV, married Henry VII and became Queen of England.

The Duchess died on 31 May 1495 and was buried in the tomb with her husband Richard and their son Edmund at the Church of St Mary and All Saints, Fotheringhay, Northamptonshire, with a papal indulgence.

She is portrayed as having deep affection for her dead sons George and Edward, but is cold and unloving to Richard, to whom she refers as a "false glass that grieves me when I see my shame in him."

The disapproving Duchess, who was known in real life as "proud Cis", is too easily overcome by her social inferiors when they whip out her apparent "secret" affair with a French archer and Elizabeth commands that she bow before her.

While contemporary notions of "courtesy" dictated extreme forms of submission to the queen, this is a Lady Cecily straight from the pages of a novel rather than the actual proud aristocrat who asserted her own right to rule.

[9] In 2016, Neville was portrayed by Judi Dench in the BBC television mini-series The Hollow Crown: The War of the Roses, in the third episode; which is based on William Shakespeare's play, Richard III.