Last warning. This is what I think happened during the deliberately omitted scene in the season 3 finale. If you don't like spoilers, please come back after you see the episode.
Reprise
Wo Fat crept up the stairs with a smile of satisfaction on his lips. At last he had cornered Shelburne, that ghost, that monster. At last Wo Fat would get his revenge on the man who killed his father.
But when he pushed open the door, he found himself facing a woman, standing defiantly holding a gun pointed at the floor.
Wo Fat was shocked to his normally unflappable core. Shelburne was the last person he ever expected to see. Shelburne was truly a ghost – a ghost from his past, a woman he thought long dead.
In his bewilderment, only one word came stuttering to Wo Fat's lips, "Mom?"