So, going out on a limb here - as I do - but nothing ventured, nothing gained

I’ve got a bunch of Robertsons in my family, so I was curious to see where this would lead…
There is a John Robertson, aged 4, b. Lonmay in the 1881 census in Lonmay. He's enumerated as the grandson of the head of the household, Jane Robertson - there are also three other children under 10 - Margaret, Joseph and Alexander, who are all children of Jane Robertson.
Following the censuses and Poor Relief registers, this Jane Robertson is Jane Watson, widow of Joseph Robertson (he died in 1880). This couple had at least three other children, including the eldest, a James Watson Robertson who was born in Gamrie in 1862, just before his parents married - he's in Longside with his parents in 1871, and in Peterhead as a farm servant in the 1881 census. He then emigrates to America around 1888 (where he married and had at least 4 children. He died in 1930 in Iowa). His mother died in 1891 in Kininmonth.
If he is John Bruce Robertson's father, he would have been pretty young - 14 or 15 - but it's not beyond the realms of possibility. Having had a look at John Robertson’s marriage to Jessie Napier in 1904, one of the witnesses is a Joseph Robertson, who could be Joseph Robertson, son of Joseph Robertson and Jane Watson - and therefore John Bruce Robertson’s uncle. Unfortunately, the addresses or occupations of the witnesses aren't included, so we can't be 100% certain - this Joseph Robertson was a blacksmith, and in Ellon in 1901.The other witness is James Napier, likely Jessie’s father (she was the daughter of James Napier and Jessie Munro). And just for clarity, the marriage registration says of John’s parents: James Robertson (farm servant) and Mary Bruce (domestic servant) - so no suggestion they were married.
As for Mary Bruce, the mother - looking at the 1877 birth record for John Robertson Bruce in Lonmay - and he is, indeed, the son of Mary Bruce, domestic servant at Mosstown in Lonmay - born 27 Dec 1876. Mary is at Mosstown in both the 1871 and 1881 censuses. She seems likely to be the Mary Bruce who was born to William Bruce and Elizabeth Rettie in Strichen on 10 Apr 1851. She’s with her parents in Strichen in 1861, and, as I say, in Lonmay at Mosstown in 1871 and 1881. Mary had at least one other illegitimate child - Alexander Bruce Ruxton, who was born in 1892 in Strichen - Mary is with Alexander in Strichen in both the 1901 and 1911 censuses.
So I think we can say with certainty, that the child born as John Robertson Bruce in Lonmay in 1876 is the son of Mary Bruce, domestic servant, and the same John Bruce Robertson who married Jessie Napier in 1904 (his place of birth is noted as Lonmay in the 1921 census). Whether James Watson Robertson is the father is, I think, still up for debate, but I’m not seeing any other obvious candidates at the moment.
Ruth