It all began late at night when Jack and Jill's parents were asleep.
Jack snuck into Jill's room while she waited for his arrival. Jack slowly opened the door for her sisters room so their parents wouldn't hear. He enters and greets his sister.

"Hello Jill you are looking so cute today" Jack says with a sly tone

"Thank you Jack" Jill says inviting him into her bed.
Jack gets into Jill's bed. They snuggle with each other. Jack makes the first move by kissing Jill in the lips.
As Jack kisses Jill on the lips Jill softly moans.
"Jack you're such a great kisser~" Jill said
Jack starts to undress Jill. As he pulls down her pants Jill's heart starts to race with excitement. Jack undressed himself as he puts his dick into his own sister.
This is is how their relationship started.