Three-year-old Alidy Clark was her father's little princess. He used to call her that when he got home from work. When he died she was devastated, and began wearing princess costumes every day.

"Every day she puts one on and whispers, 'Look, Daddy, I'm your princess," said her mom Jenna Haslam. "Her therapist calls it coping with costumes."

Alidy has a favorite: Ariel from The Little Mermaid. So 15-year-old babysitter Keegan Carnahan got an idea.

She's the babysitter Alidy loves the most, because she has pink hair just like a mermaid. Carnahan was going to do one better though.

"I went through a phase a couple years ago in which i bought a mermaid tail," said Carnahan. "It's been in my closet for a couple years so Alidy hasn't seen it."

That changed one day when it was bath time.

Carnahan surprised Alidy by showing up looking exactly like her favorite princess, and she had a little tail for her too!

Needless to say, Alidy was bubbling over with excitement, even though she normally hates bath time.

Carnahan knew how hard a time Alidy was having and her ultimate gesture won over the hearts of thousands. She tweeted out a picture that's been liked and retweeted hundreds of thousands of times over.

The joy on Alidy's face is contagious so Carnahan's mission was accomplished.

"I was so happy that she could spend 20 minutes being a worry-free little mermaid."