Featuring rap verses by Williams and a vocal hook by co-star Coco Jones, "Guardian Angel" is about "finding purpose and heading to the top," according to Disney.
"I wanna be the greatest in the world/ Not for the money or the fame or the girls," raps Williams, an actor and musician best known for his stint on the comedy series "Everybody Hates Chris."
Cyrus' reason for rhyming -- "simply 'cause I love it" -- is echoed in Coco's impassioned chorus, which plays like a plea from the lead character to his father.
"Oh, this is who I am/ I wish you'd understand," she sings. "It's time to set me free/ My guardian angel."