Born in Andhra Pradesh, India, the artist was an Overseas British subject. He was the 6th child of 7 children born to The Rev Joseph Duncan and Harriet Lucy Ostrehan, posted abroad with the British Army in Madras as a Chaplain in Holy Orders (C of E). 

Ostrehan married Eva WHITCOMBE, and they were resident at Vine Cottage, Newlyn in 1891. He exhibited with the west Cornwall artists at Dowdeswell in 1890 (See Hardie 2009). The couple left Newlyn in 1893 for Kensington, London, and in the ten years following he had paintings of six windows hung in the RA. He died, age 36 on 9 October, 1903 of cancer in Sunbury on Thames (GRO) and on his death certificate he is listed as an ecclesiastical artist.