"Your grandsire commanded it. A woods witch had told him that the prince that was promised would be born of their line."
"A woods witch?" Dany was astonished.
"She came to court with Jenny of Oldstones. A stunted thing, grotesque to look upon. A dwarf, most people said, though dear to Lady Jenny, who always claimed that she was one of the children of the forest."
This certainly appears to be the Ghost of High Heart, who refers to Jenny of Oldstones as "my Jenny". Her prophecy relates to Aerys Targaryen being wed to his sister Rhaella due to her prophecy. Interestingly, the speaker -- Ser Barristan -- refers to "the prince that was promised" quite casually, as if it's a prophecy he's familiar with.