Shawn Mendes, the serious, striking musician, emerges

NEW YORK -- When Shawn Mendes went into the vocal booth to sing "Mercy," the gravelly, deep, emotional rock song from his latest album, he discovered a new side of himself.

He found his voice.

"When I sing it, when I perform it, like everything to do with the song is completely, just like my heart races, my blood pressures rises, I get all hot," said Mendes, who was encouraged to scream some of the lyrics to bring the song to life. "It's something that's unexplainable."

"After the take, I almost wanted to cry because so much emotion poured through me and you feel it in the song," he added.

"Mercy" is one of the best representations of Shawn Mendes, the adult musician. His sophomore album, "Illuminate," showcases a matured, meticulous 18-year-old guitar player and singer who knows how to emote perfectly on a song.

He recruited Jake Gosling, the producer behind many of Ed Sheeran's hits, to help craft the album, which ranges from rock to pop to blues. Mendes, Gosling, singer-songwriter Teddy Geiger and others travelled to upstate New York to record -- living together, running in the morning and taking walks at night.

"The scene was just so right," said Mendes, who would record during breaks from touring. "It was gorgeous because we got to sit with the music, sit with the demos ... learn what we liked and learn what we didn't like."

Mendes co-wrote each of the 12 tracks, detailing some of his own personal life on the songs. The soft and pleasant "Three Empty Words" is about him staying in a relationship that ran its course. There are other songs, too, that strike with similar passion: "Don't Be a Fool" is a soulful rock classic; "Lights On" is a sweet rock song; and on the album opener, "Ruin," Mendes sings with a commanding tone: "And I'm not trying to ruin your happiness/But darling, don't you know that I'm the only one for ya."

He started writing some of the songs the day after his full-length debut, "Handwritten," was released last year. That album and his 2014 debut EP helped him establish a feverish female fan base and launched hits like "Stiches" after he broke through by singing cover songs on the social platform Vine at age 15.

But, until now, he was boxed in the category of the teen pop performer.

"I think it's very easy because of him being -- well now it's just turned 18 -- for people to sort of think of him (as a) pop star than rather a true artist," Gosling said. "The first thing when I met him ... I was really surprised by Shawn's maturity to be honest with you. He's like a wise, old man."

Even Mendes is noticing how people have begun to take him more seriously with his latest release: "Within one day, within a few hours, I feel like everything has changed. Like a switch was just turned.

"And the thing is when I first started performing live I mean, I could do it, I wasn't that impressive, but I worked so hard at the two most important things in my career ... songwriting and performing," he added.

"Illuminate," released last month, debuted at No. 1 on the Billboard charts and its first single, "Treat You Better," is a Top 10 hit; Mendes topped Spotify's 25 Under 25 list, besting Justin Bieber, Ariana Grande and Chance the Rapper; and he's honed his skills after touring with Taylor Swift and Sheeran, and has even become friends with one of his biggest inspirations: John Mayer ("He's a really great guy and helps with a lot of things I struggle with.")

And in just a few years Mendes has sold out Madison Square Garden, where he said he converted some of his young followers' parents into fans last month.

"I thought it was going to be the worst show Madison Square Garden ever saw (but) it was the best show of my entire life," he said. "I'm so proud of myself and I don't mean proud of myself in a conceited way. I truly worked really hard to get there and to make a great show."