Artist’s description from DA:

“Alternate Gender Counterparts of Heroes” is my new project! Here, characters switch roles with their soul mates (mares with stallions and stallions with mares).

Braeburn is the Alternate Gender Counterpart of AppleJack. He is a very hardworking earth pony, who likes to pick apples. He represents The Element of Honesty.

It should be mentioned here that the artist has stated on their Deviantart account that they do not consider soul mates to be strictly a romantic relationship, but also to include things like brother-and-sister bonds.