Duncan MacNaughtan was born on 4th March 1920 at Hillside, Bearsden. He had a twin, Alan, who was younger by 15 minutes.
Their father, Alan George MacNaughtan, was an architect and had married Mary Henrietta Jebb in 1918.
Comparing the house name ‘Hillside’ to the 1920 and 1940 Valuation Rolls confirms that this is 8 Grange Road; it is still known by this name today:

Note that Scotland’s People and the Bearsden War Memorial spell his surname MacNaughton but his birth record (among other sources) show clearly it is MacNaughtan:

In the 1921 Census the family was at home, with three servants to help:

Unfortunately, we know very little about Duncan. He attended Glasgow Academy. His nickname was Don. And he was training to be an architect.
In the Second World War, both boys joined the armed forces. Duncan was in the army with the 54th Light Anti-Aircraft Regiment (also the 9th Battalion, Argyll & Sutherland Highlanders) and in 1944 he served in France and Belgium after D-Day. (Thanks to Rod McKenzie of the Argyll and Sutherland Highlanders Regimental Museum for help with this.)
On 21st September, 161 Battery was sent to Boulogne to act as coastal artillery. The regiment’s history says, “Boulogne … was a shambles. The main roads had been cleared but the side roads were blocked with debris. There was no lighting, few undamaged houses, and no recreational facilities for the men.

Almost at once came tragedy. Capt MacNaughtan (Commander, F Troop) and his troop leader, Lieut. Collier, were killed during reconnaissance for fresh gun positions by a booby trap made from two six-inch shells covered by a pressure plate and buried in a side street. A brave and experienced troop commander, and one furthermore who, himself no mean piper, had taken infinite pains with the pipe band, MacNaughtan was a grievous loss. Collier, a schoolmaster by profession, was a most reliable and efficient officer. They were buried in the military cemetery at Boulogne.” (from Barker “History of the Argyll and Sutherland Highlanders 9th Battalion 54th Light A.A. Regiment 1939-45” pages 70 to 71 with thanks to David Ryan for his help).
This happened on 23rd October 1944 and they are buried side-by-side in Boulogne Eastern Cemetery. Duncan’s headstone says simply, “I hope in God”.

This is the same cemetery as Major William Watson (link), killed just over four years earlier.
Duncan’s twin brother, Alan, went to RADA and became an actor of some renown in the 1960s and 1970s. For more detail on his career see this link to the imdb website. In obituaries/biographies of him I can find online, there is no mention of his having been born a twin or of the death of Duncan.

Duncan’s father (Allan) and grandfather (also Duncan) were both architects. Duncan (senior) designed Maryhill Burgh Halls:

This is the Google Earth view from Maryhill Road, looking north-west, canal in the top right.

In the second Google Earth view I have moved along Gairbraid Avenue to try to capture the different parts of the block of buildings.
I believe Duncan had ten children, but Allan seems to have been the only one to become an architect. His best known building is probably the Students Union at Glasgow University:

Another building Bearsden people may know is Roman Court on Boclair Road:

This has already featured on the website as the home of the family of AB Cook (link).
He also designed a house in Bearsden called Elisdon for DF Nicol, a jeweller, which is very probably 4 Ralston Road:
