May not help with death or military details but here are his likely parents info.
FRANCIS, CYRIL EDWARD mmn MACKENZIE
GRO Reference: 1911 J Quarter in ISLINGTON Volume 01B Page 143
Marriages Jun Q 1905 same page with others
FRANCIS John Percival Eastbourne 2b 164
Mackenzie Beatrice Eastbourne 2b 164
1911 they are in Islington, both b 1883, no children with them, John Percival is a hotel valet
1921 free index - Cyril Edward Francis b1911 Islington, living Islington, London, Middlesex
Cyril Edward, Beatrice Eleanor, John Percival and 1 other are on this record
Some history. Maybe he was RAF?
https://en.m.wikipedia.org/wiki/MOD_St_AthanJust for info Bridgend registration district would cover St Athan, maybe they met there?
Also if they married May 1941 and son born Jan 1942 there would be only around 9 mths between, not a lot of time for meeting another potential father. Just a thought....
Cas