I think this is your great-grandfather Charles F Sadler on the 1939 Register (already mentioned previously in this thread):
https://www.ancestry.co.uk/imageview...ea&pId=9873333
At 33 Claremont Street, Edmonton, date of birth 6 Aug 1869, painter (i.e. house painter). There is a Charles F Sadler death in Edmonton Jan-Mar 1941 age 72 which is probably him.
The Charles Frederick Sadler who was in the Rifle Brigade died in 1916 in WWI, so is not the same person.