Last fall, when David Brook found out “Legacy,” a song he had co-written, would appear as track 6 on Eminem’s 2013 album “The Marshall Mathers LP 2,” he ran down Madison Avenue screaming at the top of his lungs. “It was the most exciting moment of my life,” the 2006 Marblehead High School graduate said.

That was true until February 8, when the album won the Grammy for Best Rap Album of the Year. “It was as climactic as it gets,” Brook said. “I’m still waiting for the alarm clock to wake me up and tell me it’s all a joke.”

The National Academy of Recording Arts and Sciences of the United States awards a Grammy Award, or Grammy, to recognize excellence in the creation and production of musical recordings.

Brook credits his mom, Bonnie Brook, and Steve Geyer, his Lynn music teacher during his adolescence, for his interest and success in the music industry. “David has always been an exceptional young man,” said Bonnie Brook. “Living in a small town, I took every opportunity to involve my kids in going to Boston so they felt they were part of the larger world.”

Music was one of the ways in which David expanded his horizons. He started writing songs as a middle schooler and made his first real demo while in high school. After learning that his cousin was friends with the wife of Atlantic Records CEO Craig Kallman, David begged her to pass his demo along. It was 2006 and Brook was a freshman at Northeastern University.

“I knew it was a little bit of a stretch, but I thought that maybe if his wife liked it, she would pass it off to Craig,” Brook said. “Maybe something would happen.”

Indeed, something did. The executive loved the song. He flew Brook to New York for a meeting which was leveraged to get a manager and collaborate with “some big writers and producers.” Upon graduating from college in 2011, David penned a deal with Universal Music Publishing Group.

One of his first writing sessions for Universal was with singer-songwriter Polina Goudieva. “We sat down and wrote this ballad on the piano. We thought it was a good song, but didn’t really know what to do with it.” Brook said. The song would become “Legacy.”

Polina played it for an Interscope Record executive who sent it to producer Emile Haynie, who had previously worked with rapper Eminem on his last album. Haynie loved the song and sent it to Eminem after production.

“We sent him that song in late 2011 and the album didn’t come out until fall 2013. There was a gap of two years when we didn’t know what was going on,” Brook said. The selection process is shrouded in secrecy; he knew the song was in the mix for inclusion on the album, but he didn’t know whether it was chosen. “With an artist as big as Eminem, the process is kept very close to a select few,” said Brook. “I later found out he recorded around 200 songs for the album; 16 made the cut.”

One day an employee at Universal called him and told him that the MMLP2 track list had leaked online and “Legacy” was included as Track 6 on the new album. The song included verses by Eminem, which told the story of his troubled childhood growing up in Detroit.

Brook heard the finished version for the first time when it was released to the public. “Eminem is one of my favorite artists of all time. I was expecting it to be great,” he said. The album debuted at #1 on the Billboard 200 Charts and had the second biggest first week sales of the year behind Justin Timberlake. It has sold over four million copies worldwide. “Legacy” peaked at number 44 on the U.S. Billboard Hot R&B/Hip-hop Charts.

Bonnie Brook was confident her son would succeed. “David is someone who really takes advantage of what’s there and is cognizant of how to work the system,” she said. “[Music teacher] Steve Geyer gave him incredible confidence in himself.”

Contrary to the glitz and glamor of the televised award announcements, many categories are announced via the internet on Grammy.com before the show begins. Brook found out the album won Best Rap Album of the Year when a fellow nominee texted him, “Dude, the album won.”

“My mom thought I would go on stage and be on TV for a half hour,” Brook said with a laugh.

Brook watched the Grammy Awards show with friends, his girlfriend, and his sister Alexandra (MHS ’03) at his downtown Manhattan apartment. He could have attended the event, but wanted to spend the night with the people closest to him.

When asked if he will receive the famous gold statue, David replied, “I think I get a certificate or a plaque that says, ‘Congratulations.’” The intangible benefits, however, are priceless. “I wrote a song that’s on the album that won a Grammy for Best Rap Album of the Year,” he said. “It’s been a cool year.”

To listen to “Legacy,” go to vimeo. com/78224432.