This woman "could not stand" her teacher as a kid. She just gave him a kidney.

Montana Miller, of Long Island is being hailed as a hero after donating her kidney to a man that she once described as her "sworn enemy."

(A long, long time ago, that is.)

Mitchell Grosky was her 5th-grade teacher. As a 10-year-old, Miller "absolutely could not stand him." The two of them constantly clashed throughout the school year.

But after 45 years (and a lot of life experience), Miller's feelings towards her one-time enemy have softened. Last year, when she saw on his personal Facebook that he was in the final stages of kidney disease and awaiting a donation, she was moved to action.

Miller told The Boston Globe,

I wanted to help Mitch so badly that it became almost painful.

Despite the two being different blood types, she found out that her kidney was a match for him in December, and the transplant finally took place on April 21st.

Miller wrote on her Facebook during the recovery,

The pain I'm going through now is definitely not more than I can handle.

Adding that,

It almost feels good, like this pain is something that is a privilege.

Grosky, meanwhile, says of Miller:

She is maybe the most brilliant, most creative student I've ever had in any grade level.

The transplant was a success, and Grosky is back at home with his wife while he continues to recover from the surgery.

As for Grosky, he couldn't be more grateful for the unexpected gift from a student from so many years ago. Grosky told The Globe,

Awesome has become a slang term. But awesome when you look at the Grand Canyon. Awesome is when you see pictures of the moon. She comes closest to anybody I've ever known to really being awesome, in the truest sense of the word.