You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Russian_Soviet_Federative_Socialist_Republic

Context:
On April 17, 1946, the Kaliningrad Oblast — the northern portion of the former German province of East Prussia—was annexed by the Soviet Union and made part of the Russian SFSR.

Question:
What province of Germany did Kaliningrad Oblast form a part of?

East Prussia