Not all heroes wear capes.

When self-confessed ‘super duper gay’ comic-book store clerk Mary (@saphhicgeek) found a young girl wandering the store aisles, she stepped in to help.

Little did she know her act of kindness would help a queer kid in trouble, and draw praise from Supergirl actress Chyler Leigh.

“So, I want to tell you all what happened in the store today. It’s probably the single greatest moment I have ever experienced working here,” Mary posted to Twitter.

“After the usual Saturday rush, a teenage girl comes in. She looks absolutely terrified and when I greet her she jumped. She starts going up and down the new release wall and the poor thing looks completely overwhelmed.”

Mary soon discovered that the young girl was a fan of the Supergirl TV show, in particular its gay character Alex. When Mary agreed that she loved Alex and Maggie’s relationship on the show, the girl burst into tears.

“I’m trying to figure out what the hell I did to upset her. She’s crying and I’m freaking out,” Mary posted to Twitter.

“After a minute or so, everything clicks. I’m staring down a crying baby gay. One who was having some big issues.

“I tell her that it was hard for me when I wanted to come out too. She finally stops crying and asks me if it gets easier.”

It soon transpired that Alex’s coming out story on Supergirl made the teen realise her own same-sex feelings. Not only that, the young girl was troubled by her same-sex feelings, had been having suicidal thoughts for a long time and had attempted to take her own life.

Mary wrote: “But as Alex’s arc continued she said she realized that she started to see that she could be happy, that she could be loved. She didn’t want to die anymore. For the first time, she didn’t want to die because she got to see Alex be amazing and be queer.”

The teenager hadn’t realised there was a world of LGBT comic book characters out there, but Mary was more than happy to introduce her to Batwoman, Midnighter and Renee Montoya – prominent LGBT heroes.

From the selection of books Mary picked out, the young girl could only afford one. Knowing what it felt like to be a closeted, confused teenager, Mary agreed to spend her own $60 on the remaining books.

“I was having an internal crisis at that time, because this kid was me years ago,” she wrote. “I was barely holding off my own tears. I ended up buying the other 3 for her and I make her promise me that in 10 years she’ll help another queer kid.”

Mary’s act of kindness soon went viral. Her Twitter feed was filled with people offering to reimburse her the $60 for her good deed, or pay the equivalent towards an LGBT charity of her choice. Mary chose Equality Florida and supporters began donating in her honour.

Supergirl actress Chyler Leigh even weighed in to show her support for Mary and her young fan.