Papa to Kiss in the Dark(2005)

Papa to♥KISS IN THE DARK

Munakata Mira is in love with his father, the famous Hollywood actor Munakata Kyousuke. Unknown to the public, both of them are father and son as well as lovers. When Mira turns 15 and enters high school, he faces trouble with his childhood friend falling in love with him. Also, finding out he is adopted only distresses him further. Then there's the problem of Kyousuke probably marrying a famous actress, whose son seems to have an interest in Mira.

(Source: Anime News Network)