He said the movie was boring, but I found it quite interesting. In fact, it was the best film I'd seen all year.

in 是介词，表示"在...之内"或"关于"。 fact 是名词，意思是"事实、实际情况"。 in fact 是一个固定短语，表示"实际上、事实上"，用于强调接下来要说的内容是真实情况或与之前所说的形成对比。