Wedding preparations are underway for Lower House member Shinjiro Koizumi, 38, a prominent politician who is widely seen as a potential future prime minister, and TV personality Christel Takigawa, 41.
The pair made the surprise announcement at the Prime Minister's Office on Wednesday. Their relationship was until that moment a closely guarded secret.
Separately, Koizumi wrote on his blog that Takigawa is pregnant and due to give birth early next year.
With your current subscription plan you can comment on stories. However, before writing your first comment, please create a display name in the Profile section of your subscriber account page.