Why did "Family Guy" decide it was time to kill one of its main characters Brian, the Griffin family's dog?

On Sunday, "Family Guy" fans said goodbye to one of their favorites as Stewie tearfully watched his furry friend lay dying after being struck by a car.

After Brian's death, fans took to Twitter in shock - "NO NO NO NO !!!!! I AM NOT AMUSED AT ALL!!!" and "I AM NOT OK WITH THIS FAMILY GUY DEATH. NOT OK!!!" were some of the posts.

(Photo Credit: FOX/Getty Images)

So, after 11 seasons, where Brian was a key star, why kill him off now? E! News spoke with executive producer Steve Callaghan to find out.

"This was an idea that got pitched in the writers' room and it sort of caught fire, and we thought it could be a fun way to shake things up," he told E!.

Read: 'Family Guy' Kills Brian the Dog

Now that Brian is gone, a new dog Vinny, voiced by "The Sopranos'" Tony Sirico, will join the family. Sirico was Paulie Walnuts on the iconic HBO drama. Callaghan explained why the show runners felt they needed to replace Brian right away.

"It felt like the way that this show was conceived by Seth all those years ago, it was this entire family unit including the parents, kids and a dog," he said. " So by losing Brian, it felt like a void needed to be filled both comically, and also for the interpersonal relationships between all the characters. We felt that we needed to fill that role."

He added that show creator Seth Macfarlane is a big "The Sopranos" fan, so the addition of Sirico just made sense.

" [He] always loved Tony Sirico in particular and he thought it would be fun to write a character based around his voice and his personality and just who he is as an actor," he added. "Brian was very smart and studios and intellectual, and Vinny is just a lot more of a rough around the edges."