Here is a Daily Record article about a rather nice Scottish castle for sale, that was apparently built for Laurence Bruce, half-brother of Robert I … except that we can find no evidence that he ever existed. By both the same parents, Robert’s brothers were Thomas, Alexander, Neil (all executed in 1306-7) and Edward, the King of Ireland killed in 1318. Robert had no paternal half-siblings and only a (nameless and probably died in infancy) half-sister by his mother. His Essex-born father Robert survived his mother Marjorie by about twelve years but didn’t re-marry and seems not to have had a new partner so there wasn’t even a step-brother.
Then I read that Muness Castle, on the UK’s most northerly isle, Unst in the Shetlands, was built in the fifteenth century, so a hitherto unknown brother, born by Easter 1305, must have lived to at least 1400 to order such a structure. So who was it really built for?
As the above link shows, the real Laurence Bruce lived from 1547-1617, with Stewart connections, and was probably from a branch of the great family with a brother named Robert. In any case, the Shetlands were only ceded to Scotland in 1469, as a dowry.