The last presumed victim of Jack the Ripper was a prostitute named Mary Jane Kelly on November 9, 1888. Rumors popped up that Kelly had been carrying (or had borne) a child by Arthur Sullivan.QUOTE Dan Kravetz Gilbert and Sullivan Society

https://mailman.bridgewater.edu/pipermail/savoynet/2009-December/001171.html

Arthur John Sullivan, son of the Mary Kelly candidate from Liverpool, was born in September of 1887 according to his recently-discovered birth certificate.

This puts the conception around the time that the real Mary Kelly was living in Whitechapel with Joseph Flemming. Sir Arthur Sullivan is out of the equation.

This leaves Joseph Flemming, John McCarthy, or maybe composer Michael Maybrick as possible fathers....