Apparently he was planning to visit me and surprise me for my birthday, which was the following day.

apparently 是副词，由形容词 apparent（明显的、表面上的）加上副词后缀 -ly 构成，意思是"显然地、表面上看来"。这个词常用于表示根据已知信息得出的推断或表面现象，暗示实际情况可能并非如此。