Philyra

Cronus changed into a stallion and mated with Philyra. Philyra gave birth to Chiron, the Centaur.^[H45]
Another account tells that Philyra changed into a mare to hide from Cronus, but he changed himself into a stallion and found her.^[H45]
Horrified when she gave birth to Chiron, she asked Zeus to change her into a lime-tree.^[L11]