"I know. Somehow, I've always known."
That was Leia's reply to the news that Luke Skyalker, hero of the Rebellion, last hope of the Jedi and son of Anakin Skywalker was her twin brother. But cast your mind back just four years to the Death Star, when Luke and the gang were breaking her out of detention block AA23.
Luke enters and announces himself.
"I'm Luke Skywalker, I'm here to rescue you!"
"You're who?"
"I'm here to rescue you, I've got your R2 unit, I'm here with Ben Kenobi."
"Ben Kenobi, where is he?"
"Come on!"
Is it beyond the realms of possibility that this was the moment that she refers back to in Jedi?
"Somehow, I've always known."
The always in that remark must refer to the length of their relationship, which ended 19 years before on Polis Massa and reignited on the Death Star.
Is it a stretch to think that she knew right away, but for whatever reason didn't allow, or didn't know how to organise those feelings?