More possibilities if your James was killed in action ...
Commonwealth War Graves Commission Register
Name - MILLAR , J  
Rank - Private 
Service No. 21/152 
Death Date -  01/07/1916  
Age Unknown 
Regiment - Northumberland Fusiliers 
Nationality - United Kingdom 
Grave/Memorial Ref. - VII. A. 7.
OVILLERS MILITARY CEMETERY 
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Possible:
GEORGE LIDDELL MILLER married  MARJORY REID FOREST  
on 10 MAY 1870   Duddingston, Midlothian, Scotland 
OPR 
1881 British Census  
George L. MILLER   Head   M   Male   38   Scotland   Bookseller     
Margery MILLER   Wife   M   Female   38   Scotland        
William MILLER   Son      Male   9   Alnwick, Northumberland, England   Scholar     
Thomas MILLER   Son      Male   8   Alnwick, Northumberland, England   Scholar     
Jessie MILLER   Daur      Female   5   Alnwick, Northumberland, England   Scholar     
James MILLER   Son      Male   1   Alnmouth, Northumberland, England        
Dwelling   35 Marygate 
Place Berwick Upon Tweed, Northumberland, England