After the Phantom Lord arc ends, and before the ToP arc starts (I think it's even before we find out about Loki being a Stellar Spirit). When Lucy returns home to have a conversation with her
father. We then see a scene with Lucy standing in front of Layla's grave, which had the year she died engraved into it - X777. We also see she was born in X748, so she died at age 29. The current
year is X784, and Lucy is uhhh... 17 years old, if my memory serves me right. Therefore, Lucy was born when Layla was 19, and Layla died when Lucy was 10. Not that it matters. I just thought of
pointing it out.
I'm not gonna bother going into deep details with it. See, during the conversation between Igneel and Grandine, the translators note say the the "child" they were talking about wasn't specified as any gender. It is a "mystery child" of sorts, since we don't know specifically who they were talking about. It could be Gerard. However, as I said, it is highly unlikely. I believe it's obvious Mashima intended to make it so that they were talking about Natsu. But there are more skeptical ones who believe otherwise.
We saw Igneel and Granine, Gildartz implies he saw a black dragon, which is suspected to be the Dragon King mentioned in the chat between Igneel and Granine, but like I told you, the point of this thread is not to make a correct theory but to get to Mashima's head, you did very well, as you noticed that both Natsu and Igneel share a common scar on their neck, and both Wendy and Granine are very small (Granin considered a smaller Dragon, Wendy considered nearly loli) which is by comparison to Edolas Wendy which is pretty tall.