For those wondering about that rather curious comment Percival Graves (actually Grindelwald) made to Credence Barebone about having a vision, in
Fantastic Beasts and Where to Find Them, J.K. Rowling sort of cleared that up by stating the dark wizard was - in addition to an accomplished Occlumens - a Seer.
Rowling's fairly open-ended response could mean that Grindelwald was an actual Seer - along the lines of celebrated witch Cassandra Trelawney - or one who may have had a vision or two, like her great-great-granddaughter, Hogwarts Divination Professor Sybill Trelawney.
@jk_rowling what did Graves-Grindelwald mean when he said: ”My vision showed only the child's immense power”? Is he a Seer or was he lying?
The Harry Potter author did not specify which bit of the comment Grindelwald lied about (or the entire statement), despite his desire to find and contain an Obscurus.
On a somewhat-related note, J.K. Rowling retweeted this particular post. The author never confirmed Gellert Grindelwald's country of origin, just that he went to and was eventually expelled from Durmstrang.
This may not necessarily be confirmation that Grindelwald was from Switzerland, given that the name Gellert has both German and Hungarian roots, and the name Grindelwald is German. Grindelwald was also presumably part-British, given his great-aunt was
History of Magic author Bathilda Bagshot, who lived in the English town of Godric's Hollow her whole life. Though, notably, Bathilda is a German name.
Pre-order J.K. Rowling's Fantastic Beasts and Where to Find Them in the following formats now:
• Fantastic Beasts and Where to Find Them (Amazon Exclusive) (Niffler Figurine/Blu-ray + DVD + Digital HD UltraViolet Combo Pack)
• Fantastic Beasts and Where to Find Them (Blu-ray + DVD + Digital HD UltraViolet Combo Pack) 
.jpg)
J.K. Rowling reveals Grindelwald was Seer in 'Fantastic Beasts', Harry Potter series 
