A long time ago, Star Butterfly had relinquished her wand to the rightful ruler, Eclipsa Butterfly.
But Eclipsa had given it back after finding and uncrystilizing her husband Globgor, and renewing her daughter, Meteora.
Eclipsa, as much as she wanted to rule again, (this time rightfully so) was worried that the people of Mewni would not easily accept her, her husband, and her daughter so quickly.
So she gave the wand back to Star.
"You will make better use of it than your ancestors Star. I feel you are not like them, those people that hurt my baby girl and cast me out. You are better than them, and you hold great power."
Star gently took the wand from Eclipsa's outstretched hand.
"But what if I can't help bring Monsters and Mewmans together? What if I can't-"
"Oh tush. Of course you can. I know for certain. Star, if there is anyone who can fix this disaturous world, it's you. You will be wonderful."
Star nods. "I'm sorry. For everything my mom, and the council, and, you know, everbody did..."
Eclipsa cups Star's cheek. "Don't be sorry, Love. You will lead Mewni to a new era. One where Mewmans and Monsters alike can live in harmony. And when you do, come find me. I will return to live in peace. We may rule together if you like."
Eclipsa took out her Dimensional Scissors and ripped a hole.
"And don't worry darling! Even if we are not kin by blood, I feel we are kin by soul, love, and of course, magic. So even though you may not have royal blood, I think you are noble enough in spirit. Goodbye!"
Star looked down at the wand and felt tears well up in her eyes. After all this trouble, here she was, the wand in her hand, and a mentor gone. Where was she now? And how would she rule?
Star returned to the castle, her purple wand clenched tightly in her fist.