Derby was a second-generation bat dog for the Trenton Thunder. YouTube screengrab

Monday was a sad day across the baseball world, as the Trenton Thunder announced that Derby, their famous bat-retrieving dog, passed away from cancer over the weekend. He was 9 years old.

Over the course of his life, the golden retriever received national fame and was showered with love thanks to his duties with the New York Yankees' Double-A affiliate. The crux of those duties? Fetching bats from home plate during games. Derby was even the subject of an "E:60" feature back in 2015.

As is the case with many dogs, Derby seemed to be considered more than a pet or mascot for the Thunder -- he was a member of the family. As such, the team released a statement following Derby's passing on Monday and announced plans to honor his life and memory.

"Derby was one of the biggest parts of our identity in the nine years of his life and it breaks my heart to share this news with our fans ahead of our 25th season," Thunder general manager Jeff Hurley said.

"His presence at our games and in the community was massive and every person and dog that interacted with him will miss him dearly," Hurley said.

The dog was set to celebrate his 10th birthday later this month, so that day -- Jan. 26 -- will now be recognized as Derby Day. As part of Derby Day, the team will share a special tribute video and hopes fans will share their own favorite memories with the pup on social media 

Derby was a second-generation bat dog for the Thunder, as his father, Chase, served in the role up until 2013, when he also died of cancer. Derby's own son, Rookie, is carrying on the lineage and has been serving as the team's full-time bat dog since 2016.