Or they recognise each other, but since there is no stallion to send Unico off with a batchelor group, and no stallion to perform duties to an in-season mare, hormones take over fromwild horse behaviour.
I came to the same conclusion !
G recognised his mother after three years and she recognised him. Because he is a stallion we did not turn them out together but each day he watched with calm interest as we turned his mother and sister out. Normally when he sees a strange horse mare or gelding he gets very excited and dances.
The other day quite by accident or perhaps universal design they came face to face, G tried to be the big aggressive stallion. I don't know what Dama his mother said to him but she squealed and danced and within minutes he was apologising for bad behaviour. I've never seen another horse do that to him and in such a short time.