On the previous night, SMAP's Katori Shingo who is a close friend of Yamamoto, broke the news first by congratulating the couple at the beginning of his TV Asahi programme "Sma Station!!". Katori said at the introduction which was filmed at the rooftop of TV Asahi's building that it was very cold but he had some warm news to share with everyone. He revealed that his friend Yamamoto had become a father and congratulated him and Horikita about this.
Yamamoto and Horikita got married in August last year and announced her pregnancy in June this year.
Sources: Nikkansports 1 / Nikkansports 2 / Sanspo