Guitarist Chad Gilbert – a founding member of the US rock band New Found Glory that doled out the early 2000s anthem My Friends Over You – has died aged 45.

Gilbert’s family announced his death on Sunday, saying that he “passed away peacefully in his sleep” and “left this world surrounded by friends and family and took his final breaths with his wife and mother by his side, just as he wished”.

“We are devastated and shocked by how quickly he left us, yet so grateful for how peacefully and smoothly he went,” Gilbert’s family added, without disclosing his cause of death.

In an interview with People magazine from April, Gilbert said that he had been diagnosed with stage four adrenocortical carcinoma (ACC) after doctors discovered three brain tumors, including one “the size of a walnut”. That discovery came as he underwent treatment for metastatic pheochromocytoma – a type of adrenal cancer – since 2021.

“On [27 February] I had successful brain surgery and have been recovering in the hospital since,” Gilbert wrote on Instagram in March. “I regained function of my left hand immediately. My radiation oncologist described it like this: ‘This is not a fatal blow and not the end of your story, just the beginning of a new chapter.’”

Explaining his ACC diagnosis, his wife, Lisa Cimorelli, told People magazine: “All his treatments were working on his whole body, but they don’t cross the blood-brain barrier. So that’s why this was kind of like the last frontier of a place for things to grow wild, which is unfortunate.”

Gilbert revealed in August on Instagram that he “was crushing it and gaining weight” when “suddenly I couldn’t sleep and felt like I couldn’t breathe”.

“So I went to the ER and discovered I had 4.5 liters of fluid in my lungs,” Gilbert continued. “So lucky I went in. I stayed for [five] days and they put a needle in between my ribs to drain all the fluid. Not a good time. Now I’m back to the beginning building my strength. But thankful for the nurses and doctors that found it. Definitely kicked my butt. Hoping to feel like myself again soon.”

After Gilbert’s death, his family wrote: “The amount of visitors that crowded the hospital lobby at a moment’s notice is a testament to how beloved and cherished Chad was, and always will be. He was a legendary musician, but his favorite accomplishment was being a husband and father. His biggest dreams came true.”

Gilbert’s family wrote that his survivors include his wife; his daughter, Lily; his mother, Jackie; and his brother, Brian.

Similarly, Gilbert’s bandmates Jordan Pundik, Ian Grushka and Cyrus Bolooki wrote: “Chad’s guitar playing, songwriting, humor, and relentless drive helped shape New Found Glory for nearly three decades.

“Through more than a dozen albums, endless tours around the world, and more accolades than we ever could have imagined, Chad challenged all of us to grow as musicians, performers, and human beings. While we are devastated to lose him, we are so grateful for the incredible life he lived, the memories we shared, and the brotherhood we had.

“His influence will always be part of New Found Glory and his spirit will be felt on every stage we stand on, with every note we play.”

Founded in Coral Springs, Florida, in 1997, the band has been largely celebrated as a one of the most influential pop-punk bands of the early 2000s. The band has been touring throughout the summer, with several more shows scheduled across cities including Orlando, Florida, and Sacramento, California.

New Found Glory’s My Friends Over You and its lyrics about prioritizing one’s friendships above blossoming romance with someone else resonated with many teens at the beginning of the 21st century. Some of the band’s other signature songs included Hit or Miss and All Downhill From Here.

The band has 14 studio albums to its name, including Listen Up!, the most recent one.