Mother Shipton

Who was Mother Shipton? Some people consider her the most famous prophet in the last 1000 years, after Nostradamus. Probably she is even the most famous prophetess in the world's history. While some think she really existed and was a soothsayer or maybe an astrologer who predicted facts (most of them regarding the 17th century or about our own future), others believe she is no more than a legendary witch, a legend slowly built over the centuries. What's the truth behind Mother Shipton?