Photograph showing head and shoulders portrait of Mr Turnbull, with long grey beard and cap. The photograph is a vignette and has been cropped into an oval.

John Robson Turnbull was appointed Clerk of the Works for Windsor Castle, with responsibilities including the Royal Mews and the buildings in the Home Park, in 1846. He held the position until his death twenty years later. One particular task was superintending the erection of a temporary building attached to St George's Chapel for the use of the Royal Family at the time of the marriage of the Prince of Wales and Princess Alexandra of Demark, which took place in the Chapel on 10 March 1863.