The castle was inherited by Sir Alan de Cathcart, who was the son of Duncan's sister.

[1] The tower was at a time thought to have Pictish origins,[2]: 143  and Robert Burns had referred to Sundrum as "an ancient Pict-built mansion" in his poem "The Vision" in 1785.

The castle was built on land gifted to Sir Duncan by King David II in 1370 and was a rectangular tower.

[4][5] Sir Duncan was married to Eleanor de Brus (now translated as Bruce), Countess of Carrick, but died without a male heir.

[2] The great hall of the castle was used for official business, whilst the floor above it was used as a private living space.

[6] The Wallaces of Sundrum were in possession of Caprington Castle from the late 14th century to 1400, when a daughter of Sir Duncan married and it passed to the Cunninghams.

[2]: 49  By the end of the 14th century, Sir Alan de Cathcart took possession of the castle, with the consent of King Robert II of Scotland.

There is some inconsistency over the date it was sold, with sources giving it as 1753[6] whilst others claim it went straight to the Hamiltons in 1750.

This child, Alexander Waters, learned to be a stone mason, and eventually started his own family settled on the Sundrum estate.

Salopian Estates intended to renovate it as part of an "enabling development" with the building of new houses nearby.

[9] The developments were objected to by some of the local residents,[27] as it included the destruction of the original drive and an area of woodland.

The developers received £500k from Historic Scotland in 1995, though were thought to have privately profited from the sales of the individual properties.

[19] Wallace Tower, the castle's keep, was owned by landlords Graham and Patricia Cathcart Waddington in 2018.

[14] A selection of photographs and documents relating to Sundrum Castle in the 20th century are held at the Ayrshire Archives Headquarters.

[30][31] Sundrum Castle is located 1.5 kilometres (0.93 mi) north of Coylton, South Ayrshire, Scotland, and sits within an approximately 85 acre estate.