When the Dawn Treader returns from the second island
Sansa is waiting to welcome Caspian home in a way that ends up being not entirely proper though mindful of his promise to her father.
What isn't mindful is them falling asleep afterwards and then having to hurry back to Summerfell with Caspian determined to take responsibility,
Ned is waiting for them having known just where she has been, and he tells Sansa to be home before dark and reminds Caspian that Sansa hasn't passed into his protection just yet. But Eddara interrupts to say her first word which surprises everyone but thrills Sansa and Caspian when it is 'Dada'.
The first thread is locked for content.
Dated the evening the DT returned and the morning after.