Archibald may not be the father of Duncan. From Duncan in ancestry it does show Archibald as the father; however, when you open Archibald, it does not show a Duncan as a son.
https://www.familysearch.org/tree/pedigree/landscape/K64P-5RX
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Brooke is 26 degrees from Herbert Adair, 22 degrees from Richard Adams, 24 degrees from Mel Blanc, 27 degrees from Dick Bruna, 26 degrees from Bunny DeBarge, 32 degrees from Peter Dinklage, 26 degrees from Sam Edwards, 24 degrees from Ginnifer Goodwin, 29 degrees from Marty Krofft, 21 degrees from Junius Matthews, 22 degrees from Rachel Mellon and 20 degrees from Harold Warstler on our single family tree. Login to find your connection.