m. (1) Anne Stirling, (2) Unknown (Family Search has 272 marriages of Robert Thomsons from 1765 when Anne died over the next ten years so it is impossible to guess who his second wife was).

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Only the birth of a son George to him and Anne can be found on the Scots or Family Search records.
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In the life of George Thomson by J Cuthbert Hadden, pub 1898, the author states that Robert marriage again after his first wife’s death and in 1772 he and he new wife had a son Keith.  No record can be found of this marriage but there are three baptisms on FamilySearch between 1770 and 1774, though none have a forename and only one has the mother named, a Mary Ovenston.

So I have no real evidence either for the second wife or for Keith.

Nothing about Keith or the second wife can be found on Scotland’s people or FindMyPast.
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This may be their marriage index:

Name Robert Thomson
Spouse's Name Anne Stirling
Event Date 14 Dec 1755
Event Place Edinburgh Parish, Edinburgh, Midlothian, Scotland
Spouse's Father's Name Henry Stirling

Considering it was 14 months later that George was born to Robert and Anne, it think this is highly likely to be their marriage record.
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