Chicago Teen Sings for Pope Francis, Reveals She 'Really Couldn’t Say No'

— -- The day turned out to be extra special for Chicago, Illinois, student Valerie Herrera, who had the opportunity to sing before Pope Francis Monday.

Herrera, 17, a senior at Cristo Bey Jesuit High School, joined Americans chosen from all over the U.S. in a virtual audience with the pope via satellite. The event was moderated from inside the Vatican by ABC News' anchor David Muir.

Herrera said today on "Good Morning America" that she did not know she would have the chance to even speak with the pope until just moments before.

"They told me ...‘Oh, you’re going to be talking to the pope,’ and I was like, ‘What? Really?,'" Herrera recalled. "I thought they were joking and then I guess it was the real deal."

When it was her time to speak, Herrera told the pontiff that she'd struggled with vitiligo, an autoimmune disease that causes white spots on the face and body, since she was 4 and that she'd endured bullying for years.

The eldest of four children born to parents from Mexico, Herrera said she was very active in her church and joined her church choir. Thanks to singing and the support of her family, she told Pope Francis, through tears, that she'd finally learned to be more comfortable with herself.

Then she got a surprise request from the pontiff.

"May I ask for you to sing a song for me?" he said. "Be courageous."

After a pause and encouragement from the audience, Herrera performed, singing "Junto a Ti Maria (Next to You, Maria)."

"Well I didn’t expect it to happen and so it just happened and so I really couldn’t say no," Herrera said of the moment, adding that she chose the song because it was one her mom had taught her as a child in the choir.

"It was just like the first song that kind of popped in my head," she said. "At first I had like no clue how to start it off. I couldn’t remember the first words."

"I looked back to my mom, because she was sitting in the crowd, and I was like, 'Okay, she’s here and I can do it,'" Herrera added. "I guess just looking at her gave me the courage."

Afterward, Pope Francis thanked her for singing.

Herrera, who will be the first member of her family to attend college and plans to become a pharmacist, said she also received words of encouragement from her classmates.

"They would send me messages or they’d just text me, saying, ‘Oh my gosh, you did beautifully. You did such a great job...We’re so proud of you...I knew you could do it,'" Herrera said. "It was just a really good experience."