Ancestry have many entries for Rees's in The Boer War. Below is one, - but with no dates or full name, it's a bit like looking in the proverbial haystack(!)
Romilly.

W J Rees
Casualty Type: Died
Casualty Date: 4 Nov 1900
Casualty Place: Germiston
Rank: Sergeant
Force: South Africa Field Force
Regiment: Welsh Regiment
Battalion: 1st Battalion
Number: 7323