Hip-hop industry fixure/veteran New York City DJ Big Kap (born Keith Carter) passed away this morning from a heart attack at the age of 45. NYC DJ Funkmaster Flex broke the news via two Instagram pictures, both captioned, “Rest In Peace Big Kap.”

Kap, who was slated to host an event tonight, has quite a dynamic history with Flex. Not only were they founding members of the Flip Squad DJs (alongside Mark Ronson, Cipha Sounds, Mister Cee and Doo Wop), the pair released a compilation album in 1999, The Tunnel.

Even though it was a compilation effort, the album broke quite a few barriers in way other studio albums couldn’t. The Tunnel formally presented “Live Freestyle,” the hip-hop classic with rap gods Biggie Smalls and Tupac Shakur trading verses in the ultimate rap cypher. “Where Brooklyn at?? Where Brooklyn at??…” How could anyone forget?

The Tunnel also featured songs from every important hip-hop artist in the game during that era: Snoop Dogg, Ruff Ryders, Nas, Jay Z, LL Cool J, Mary J. Blige, Kool G Rap, Lil’ Kim and Wu-Tang Clan.

As the unfortunate news started to trend on social media, many of Kap’s industry friends and fellow rap comrades continued to lend their genuine condolences to his family.

Hot 97 radio personality Peter Rosenberg shared his thoughts after learning of his passing. “Woke up to terrible news today. We lost Big Kap. Not only a great DJ, key part of the Flip Qquad and big dog pit bulls, an incredible talker with a unique and awesome voice but more than anything—great guy… Always good for a warm smile and a sincere conversation… Was always very fond of this guy ever since I met him… RIP brother… Sending love and positive vibes to his family, @funkflex, @ciphasounds and all the pit bulls and Flip Squad.”

Rap icon, LL Cool J posted on Instagram: “I always respected you… I still do. My love to your family… Rest eternally homie. #bigkap.” Questlove, Sway, DJ Khaled and De La Soul were among other hip-hop illuminaries sending out their condolences.