Cináed mac Duib (Modern Gaelic: Coinneach mac Dhuibh) anglicised as Kenneth III, and nicknamed An Donn, "the Chief" or "the Brown", (before 967–25 March 1005) was King of Scots from 997 to 1005. He was the son of Dub (Dub mac Maíl Coluim).
Banquo, a fictional person, was said to have flourished in the reign of King Duncan, and along with his sovereign was murdered by Macbeth in 1043, leaving an only son, Fleance, who also was a fictional person. 
Both Banquo and Fleance figure prominently in Shakespeare's play, MacBeth.
↑ 2.02.12.2 The Stewart Society. The Story of the Stewarts. Edinburgh: George Stewart & Co, 1901. Cited by Stewart DNA Conversations. Stewart Ancestry Re: Stewart-DNA R1B1 & I, I2B1 Haplotypes. Accessed Jan 12, 2018 jhd
It may be possible to confirm family relationships with Kenneth III by comparing test results with other carriers of his Y-chromosome or his mother's mitochondrial DNA.
Y-chromosome DNA test-takers in his direct paternal line on WikiTree: