As long as Bryke is randomly revealing stuff, I’m just gonna throw out an “unofficial” headcanon here. You may or may not support it, but if I’m right god help the fandom.
(PS: My timelines may be a bit off here, so feel free to dispute!)
Because Suki died young, Sokka sank into an extreme depression for very long time. To keep himself distracted, he threw himself into his work and helping out with his nieces and nephews. His favorite child, however, was Lin–and as such he and Toph spent a lot of time together and developed a special bond. One night, when he was feeling particularly down, they had a long, heartfelt talk that ended in them doing some things they probably shouldn’t have done. They never spoke of it again, and it probably would have remained behind closed doors if Toph hadn’t become pregnant. But before she could tell Sokka that Suyin was his, he was killed by the Red Lotus.Toph was unsure of how the others would react, so rather than coming clean with them, she kept Sokka’s last secret. No one ever found out. Not even Katara.