On the 24th of August, 1914, during World War 1, Captain Robert Campbell of the British Army's 1st Battalion East Surrey Regiment was captured while serving on the front line.
He was shipped off to a camp for prisoners-of-war in Magdeburg, Germany. During his time there, he received word that his mother was dying of cancer. Wishing to see his mother one last time before she died, Campbell wrote heartfelt letter to the German Kaiser.
Surprisingly, the Kaiser accepted his request - as long as he returned. Campbell gave his word and returned to the UK - likely through the Netherlands - and spent time with his dying mother, who passed away in February 1917.
Upon her death, he kept his word and returned to German captivity. Most surprisingly, however, is that it was reported that Campbell then tried to escape soon after his return.
Unfortunately, no other British prisoners in German captivity were granted compassion of this sort, after the British rejected a similar request from a German prisoner-of-war called Peter Gastreich.