« Reply #4 on: Thursday 25 June 09 15:52 BST (UK) »
think I can see William on the 1911. If you use the advanced search, search on Annie Prosser with William in the household, year of marriage 1906, in Glamorgan only 1 entry shows up in Pontypridd registration district . You could double check with your mother's name as a household member.
If you find that he was born in Monmouthshire, I have a possible family
1901 Tillery Rd, Abertillery RG13/4936 folio 50 pg 40
John Powell head mar 50 colliery labourere above ground b. Brecon town
Sarah wife 47 b. Blaenavon
James Prosser steson 27 coal haulier below ground b. Blaenavon
George Prosser stepson 20 coal haulier below ground b. Blaenavon
William Prosser stepson 18 coal labourer below ground b. Blaenavon
Elizabeth A Powell dau 11 b. Cwmtillery
1891 in Cwmtillery RG12/4354 folio 16 pg 40
1881 11 Coedcaecradock, Blaenavon RG11/5237 folio 74 pg 15
John Prosser head mar 30 haullier b. Llanfoist
Sarah wife 28
James son 7
John son 5
Sarah Jane dau 3
Thomas son 1
all born Blaenavon except where stated
possible death reg
John Prosser 35 march qtr 1885 Bedwelty vol 11a pg 64
Cornwall: Allen, Bevan, Bosisto, Carnpezzack, Donithorn, Huddy, James, Retallack, Russell, Vincent, Yeoman
Cards: Thomas (Llanbadarn Fawr)
Glam: Bowler, Cram, Galloway, James, Thomas, Watkins
Lincs: Coupland, Cram
Mon: Cram, Gwyn, John, Philpot, Smart, Watkins
Pembs: Edwards (St. Dogmael's)
Yorks: Airey, Bowler, Elliott, Hare, Hewitt, Kellett, Kemp, Stephenson, Tebb