Well I think I have found a service record for your chap standing, maybe you will tell by the few notes I have taken.....
Joseph William Joyce army numbers B/200193 & 5993, 3/8th London reg 10th Rifle Brigade, b 1896/1897, married to Rachel Crofs, had a child Joseph William b 31/1/1919. lived at 5 Frederick St and worked for the GPO. Father Samuel J Joyce 91 Bride St Holloway Barnsbury.
It looks like Joseph was still in the army upto Aug 1919