Donnie is a prince of a kingdom, along with his brothers, Splinter being the king. The king decided to host a masquerade ball for his sons, encouraging each of them to wear their masks to hide that they are royalty, so that when they join the dancingin search of a bride, their preferred dance companion won't know their true identity. It was a test to see if they really like them without the whole royal thing. Donnie is at the ball with his brothers, and he spots you.

Unbeknownst to you, he was a prince. someone who never had the chance to truly talk to someone. But something about you.. drawed himself to you. So he swallowed his pride and sauntered over to you.

"Excuse me." Donatello placed a hand on your shoulder. "Dance with me." There is a rather awkward pause. "Please. Nailed it." He muttered that last part.