1842 marriage John Mitchell & Ann Bowman
This marriage was in the parish of Dun.
There are baptisms of children to John Mitchell and Ann Bowman, all in Dun: James 1842, William 1844 and Alexander 1846.
It is just conceivable that it's the same couple.
1840: birth of daughter Agnes in Tannadice
1841: John, Ann and Agnes living together in Tannadice
1842: John and Ann marry in Dun
1842: baptism of son James in Dun
1844: baptism of son William in Dun
1846: baptism of son Alexander in Dun
1846-1851: John dies and Ann and Agnes move to Forfar
This does require some explanations, however.
In particular, it requires John and Ann to be living together openly as husband and wife in her birth parish before they were married. That seems to me to be unlikely?
Fortunately the evidence to disprove it wasn't too hard to find.
1851 Census, Middle Drums, Brechin: John Mitchell, 30, born Maryton; wife Ann, 30, born Ballater: sons James, 8; William, 6; and Alexander, 4, all born Dun.