Malcolm Turnbull and his wife Lucy have laid flowers at the grave of her great uncle on the Western Front.
Roger Forrest Hughes was a newly married young doctor when he enlisted in the AIF in 1916.
Within five days of arriving on banks of the River Somme he was hit by a shell while treating a wounded digger.
Mr Hughes died at the age of 26 in the arms of his brother, the fighter ace Flight Lieutenant Geoffrey Hughes, whose squadron was nearby.
Seven weeks later Mr Hughes' wife, Eileen Maher, gave birth to their son.
Mr and Mrs Turnbull left flowers at his grave in the Heilly Station Cemetery, not far from Amiens on the Western Front.
