A British officer captured during World War I was granted leave to visit his dying mother on one condition - that he return, a historian has discovered.
And Capt Robert Campbell kept his promise to Kaiser Wilhelm II and returned from Kent to Germany, where he stayed until the war ended in 1918.
Historian Richard van Emden told the BBC that Capt Campbell would have felt a duty to honour his word.
It also emerged that Capt Campbell tried to escape as soon as he returned.
Mr van Emden said it was "surprising" that Capt Campbell was not blocked from returning to Germany from Britain.
The Daily Mail reported that after the war Capt Campbell returned to Britain and served in the military until 1925.
He then rejoined when World War II broke out in 1939, serving as the chief observer of the Royal Observer Corps on the Isle of Wight. »