Sorry to bear bad news, but I think you have the wrong death there. It's not easy knowing where registration district boundaries are in a city like London, but I think these entries may be what you're after:
William King - Jun qtr 1861 Kensington Reg Dist, 1a 29 (age 76)
Elizabeth King - Sep qtr 1868 Kensington Reg Dist, 1a 41 (age 70)
They both died in the Paddington area, so the Kensington district seems at least as likely as St Pancras - see
https://www.ukbmd.org.uk/reg/districts/kensington.html