"As a matter of fact" / "in my opinion" -- 한국말로 뭐예요?
예를 들어서:
"As a matter of fact, I arrived in Korea last Friday."
"In my opinion, Daejeon is a beautiful city."

Question

Answer

As a matter of fact = 사실은
"As a matter of fact, I arrived in Korea last Friday."="사실은, 지난 금요일에 한국에 도착했어요."

In my opinion = 내 생각에 (informal), 제 생각에 (formal) 
"In my opinion, Daejeon is a beautiful city." = "제 생각에 대전은 아름다운 도시에요."