Captain O'Shea knew about the affair, challenged Parnell to a duel in 1881 and initially forbade Katharine to see him, although she claimed that he encouraged her in the relationship. However, he kept publicly quiet for several years. His reasons for filing for divorce in 1889 was a matter for speculation. He may have had political motives. Alternatively, it was claimed that he had been hoping for an inheritance from Katharine's rich aunt whom he expected to die earlier, but when she died in 1889 her money was left in trust to cousins.
Although their relationship was common knowledge among politicians, public knowledge of the affair in an England governed by " Victorian morality" with a "nonconformist conscience" created a huge scandal, as adultery was prohibited by the Ten Commandments. At that time, politicians were supposed to lead by example. This led to Parnell being deserted by a majority of his own Irish Parliamentary Party and to his downfall as its leader in December 1890. Katharine and Parnell married shortly after her divorce from Captain O'Shea. With Parnell's political life and his health essentially ruined, he died at the age of 45 in Brighton in October 1891, less than four months after their marriage. The cause was most likely coronary heart disease inherited from his grandfather and father, who also died prematurely.
Katharine published a biography of Parnell in 1914 as "Katharine O'Shea (Mrs Charles Stewart Parnell)", so we may assume that this is the name by which she preferred to be known, though to her friends she was known as Katie O'Shea. Parnell's enemies, in order to damage him personally, called her "Kitty O'Shea" because at that time "kitty", as well as being an Hiberno-English version of Catherine/Katherine/Katharine, was also a slang term for a prostitute. She lived the rest of her life in relative obscurity, and is buried in Littlehampton, Sussex, England.
Henry Harrison (MP) who had acted as Parnell's bodyguard and aide-de-camp, devoted himself after Parnell's death to the service of his widow Katharine. From her he heard a completely different version of the events surrounding the divorce issue from that which had appeared in the press, and this was to form the seed of his later two books defending Parnell published in 1931 and 1938. They had a major impact on Irish historiography, leading to a more favourable view of Parnell’s role in the O’Shea affair