Question: In addition to Donalbain, who else is a son of King Duncan in Shakespeare's Macbeth?

Context articles: Malcolm (Macbeth)
King Duncan (disambiguation)
Donalbain (Macbeth)
King Duncan
Inverness
David Thewlis
Duncan I of Scotland
Pankaj Kapur
Three Witches
Banquo

Malcolm is a character in William Shakespeare's "Macbeth" (c. 1603–1607).
 The character is based on the historical king Malcolm III of Scotland, and is derived largely from the account in "Holinshed's Chronicles" (1587), a history of Britain.
 He is the elder son of King Duncan, the heir to the throne, and brother to Donalbain.
 In the end, he regains the throne after mustering support to overthrow Macbeth.
King Duncan is a character in William Shakespeare's play "Macbeth".
Donalbain is a character in William Shakespeare's "Macbeth" (c. 1603–1607).
 He is the younger son of King Duncan and brother to Malcolm, the heir to the throne.
 Donalbain flees to Ireland after the murder of his father for refuge.
King Duncan is a fictional character in Shakespeare's "Macbeth."
 He is the father of two youthful sons (Malcolm and Donalbain), and the victim of a well-plotted regicide in a power grab by his trusted captain Macbeth.
 The origin of the character lies in a narrative of the historical Donnchad mac Crinain, King of Scots, in Raphael Holinshed's 1587 "The Chronicles of England, Scotland, and Ireland," a history of Britain familiar to Shakespeare and his contemporaries.
 Unlike Holinshed's incompetent King Duncan (who is credited in the narrative with a "feeble and slothful administration"), Shakespeare's King Duncan is crafted as a sensitive, insightful, and generous father-figure whose murder grieves Scotland and is accounted the cause of turmoil in the natural world.
Inverness ( ; from the Scottish Gaelic: "Inbhir Nis" ] , meaning "Mouth of the River Ness") is a city in the Scottish Highlands.
 It is the administrative centre for the Highland council area, and is regarded as the capital of the Highlands.
 Inverness lies near two important battle sites: the 11th-century battle of Blàr nam Fèinne against Norway which took place on The Aird and the 18th-century Battle of Culloden which took place on Culloden Moor.
 It is the northernmost city in the United Kingdom and lies within the Great Glen (Gleann Mòr) at its north-eastern extremity where the River Ness enters the Moray Firth.
 At the latest, a settlement was established by the 6th century with the first royal charter being granted by Dabíd mac Maíl Choluim (King David I) in the 12th century.
 The Gaelic king Mac Bethad Mac Findláich (MacBeth) whose 11th-century killing of King Duncan was immortalised in Shakespeare's largely fictionalized play "Macbeth", held a castle within the city where he ruled as Mormaer of Moray and Ross.
David Thewlis (born David Wheeler; born 20 March 1963) is an English actor, director, screenwriter, and author.
 His most commercially successful role to date has been that of Remus Lupin in the "Harry Potter" film series.
 Other notable performances include the films "Naked" (for which he won the Best Actor award at Cannes Film Festival), "Dragonheart", "Kingdom of Heaven", "The Boy in the Striped Pyjamas", "The Theory of Everything", "Black Beauty", "Macbeth" (as King Duncan) and "Wonder Woman".
 He has also done voice work in the films "James and the Giant Peach" (1996), "The Miracle Maker" (2000), and "Anomalisa" (2015).
 Thewlis has combined major motion picture work with prominent television roles, including playing Cyrus Crabb in the television miniseries "Dinotopia" and antagonist V.M. Varga in the third season of "Fargo."
Donnchad mac Crinain (Modern Gaelic: "Donnchadh mac Crìonain"; anglicised as Duncan I, and nicknamed An t-Ilgarach, "the Diseased" or "the Sick"; ca. 1001 – 14 August 1040) was king of Scotland ("Alba") from 1034 to 1040.
 He is the historical basis of the "King Duncan" in Shakespeare's play "Macbeth".
Pankaj Kapur is an Indian theatre, television and film actor from Ludhiana, Punjab, India.
 He has appeared in several television serials and films.
 His most acclaimed film roles to date have been that of Inspector P.K. in "Raakh" (1989), Dr. Dipankar Roy in "Ek Doctor Ki Maut" (1991) and Abba ji, (based on Shakespeare's King Duncan) in Vishal Bhardwaj's adaptation of "Macbeth"; Maqbool (2003), all three roles which got him National Film Awards.
The Three Witches or Weird Sisters or Wayward Sisters are characters in William Shakespeare's play "Macbeth" (c. 1603–1607).
 They hold a striking resemblance to the three "Fates" (in Greek mythology), and are, perhaps, intended as a twisted version of the white-robed incarnations of destiny.
 The witches eventually lead Macbeth to his demise.
 Their origin lies in "Holinshed's Chronicles" (1587), a history of England, Scotland and Ireland.
 Other possible sources, aside from Shakespeare's imagination itself, include British folklore, such contemporary treatises on witchcraft as King James VI of Scotland's "Daemonologie", the Norns of Norse mythology, and ancient classical myths of the Fates: the Greek Moirai and the Roman Parcae.
 Productions of "Macbeth" began incorporating portions of Thomas Middleton's contemporaneous play, "The Witch", "circa" 1618, two years after Shakespeare's death.
Lord Banquo , the Thane of Lochaber, is a character in William Shakespeare's 1606 play "Macbeth".
 In the play, he is at first an ally to Macbeth (both are generals in the King's army) and they are together when they meet the Three Witches.
 After prophesying that Macbeth will become king, the witches tell Banquo that he will not be king himself, but that his descendants will be.
 Later, Macbeth in his lust for power sees Banquo as a threat and has him murdered; Banquo's son, Fleance, escapes.
 Banquo's ghost returns in a later scene, causing Macbeth to react with alarm during a public feast.