Hi Mel,
Just to summarise

So before he met Ms COX, Alexander Cyril was already married to Dorothy who had several children from a previous marriage (see headstone where he is their stepfather)
He met Ms COX and there was a birth in HAY.
Your father.
Alex was aware of and acknowledged this boy when he was 27 visited him from time to time.
Presumably Ms COX raised the boy while Alexander Cyril had more children with his wife.
You have not met any of Alexander's other children.
Do I have this right?