The future US president hilariously confused European Council President Donald Tusk with European Commission President Jean-Claude Juncker in a recent interview.
And in further embarrassment to the Brussels club, it appeared Mr Trump did not even know the names of the EU bigwigs.
This is despite Mr Trump having long talks with Mr Tusk back in November, where he thanked the EU president for his invitation to Europe and promised to visit in the Summer.
But during an interview with German newspaper, Bild, the business tycoon said: “I have spoken to the head of the European Union, a very pleasant gentleman called me.”
To which he was asked: “Mr Juncker?”
And Donald Trump replied: “Yes, to congratulate me on the election.”
However Mr Trump had never spoken with Mr Juncker.
The news is likely to ruffle feathers in the now 27-member bloc who are already reeling from comments made by Mr Trump.
The president-elect, who will be sworn in the White House on Friday, this week branded NATO as “obsolete” and predicted the EU would eventually tear apart.
In a hard-hitting interview, he also unleashed a volley of verbal attacks on Europe and criticised German Chancellor Angela Merkel’s “catastrophic” refugee open door policy.
Mrs Merkel was quick to swipe back in response, saying: “We Europeans have out fate in our own hands”.