On 8 September 2022, she became the oldest living member of the British royal family following the death of Queen Elizabeth II.

In her final year at Runton Hill, she was formally elected music secretary; in this role, she organized school recitals in Norwich.

[12] On 8 June 1961, the couple married at York Minster, the first royal marriage in that location in 633 years (the last one being between Edward III and Philippa of Hainault).

[13] Guests included actors Noël Coward and Douglas Fairbanks Jr. as well as members of the British, Greek, Danish, Norwegian, Yugoslavian, Romanian, and Spanish royal families.

[13] Her white silk gauze dress was designed by John Cavanagh, used 273 yards of fabric and had "a high neckline and long sleeves and a commanding train".

[15] The couple have three living children: Katharine had a miscarriage in 1975[17] owing to rubella and gave birth to a stillborn son, Patrick, in 1977;[17][18] this loss sent her into a severe depression about which she has spoken publicly.

"[18] The Duchess moved to the married quarters in Hong Kong and Germany while her husband was serving in the military.

[5] The couple later took numerous royal engagements on behalf of the Queen, including the Ugandan independence celebrations and the coronation of the King of Tonga.

[5] Reports by the BBC stated that the Duchess suffers from coeliac disease and Epstein–Barr virus, whose symptoms resemble those of ME (myalgic encephalomyelitis, also known as "chronic fatigue syndrome").

In 1999, the Duchess was refused permission to seat the 12-year-old son of a bereaved friend in the Royal Box at the All England Lawn Tennis and Croquet Club.

[26] Despite her decision to stay away from public life, the Duchess continued to appear at major events including the wedding of Prince William and Catherine Middleton in 2011, the concert at Buckingham Palace and thanksgiving service at St Paul's Cathedral during the Queen's Diamond Jubilee celebrations in 2012, and the wedding of Prince Harry and Meghan Markle in 2018.

[29] In December 1989, Katharine was a guest on the BBC Radio 4 programme Desert Island Discs, choosing Mozart's Ave verum corpus (sung by the Swedish Radio Choir with the Berlin Philharmonic), a DIY manual, and a lamp with solar batteries as her favourite song, book and luxury item respectively.

[30] In keeping with her withdrawal from full royal duties in 1996, the Duchess took a position as a music teacher in Wansbeck Primary School in Kingston upon Hull.

Katharine is among the co-founders of Future Talent, a charity that helps young children with low-income backgrounds pursue a career in music.

[40] In 2011, close associates of Jonathan Rees, a private investigator connected to the News International phone hacking scandal, stated that he had penetrated Katharine and Edward's bank accounts.