She’s a big sister now! And Shiloh Jolie-Pitt was on her best — and sweetest — behavior when she was introduced to her new twin siblings the day after their emotional delivery on July 12.

As her weary parents, Brad Pitt and Angelina Jolie, beamed with pride, the wide-eyed 2-year-old greeted tiny brother Knox Leon and sister Vivienne Marcheline with smiles and kisses.

“They weren’t planning on having Shiloh see Angie and the babies so soon, but she couldn’t sleep or eat until she saw her Mommy,” an insider tells Star.

As Angie, 33, held the newborns, Shiloh first stared then smiled. She was put on the bed next to them and kissed them on the forehead.

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