Valmiki Ramayana Ayodhya Kanda Sarga 66 Shloka 11

वृद्धश्चैव aged, अल्पपुत्रश्च not having sons, सोऽपि that Janaka too, शोकसमाविष्टः overpowered by grief, वैदेहीम् Sita, अनुचिन्तयन् constantly thinking, जीवितम् life, त्यक्ष्यति ननु will give up indeed.

Old and sonless Janaka, constantly thinking of Sita and overpowered with grief will surely give up his life.