Sophia Bush is mourning the loss of her ex boyfriend, Google engineer Dan Fredinburg, who was killed in the avalanche on Mount Everest following the massive Nepal earthquake on Saturday.

Dan Fredinburg Killed In Mt. Everest Avalanche

Fredinburg died Saturday after suffering a head injury, according to a statement posted on his official Instagram account by his sister, Megan. He is one of an estimated 4,000 dead as a result of the 7.8 earthquake and 6.7 tremor that occurred Sunday. 18 people were killed as a result of the avalanche on Mt. Everest, three of which have been confirmed as Americans.

Fredinburg was climbing Mt. Everest with three fellow Google employees, who both survived the avalanche. “He had this way of making the people around him just feel special without even trying, and make people feel like they could accomplish anything they wanted,” his girlfriend Ashley Arenson told CNN.

Sophia Bush Posts Tribute To Fredinburg

Fredinburg’s famous ex, Bush, who currently stars on NBC’s Chicago PD, took to Instagram to share her grief. Though the two split in 2014 after almost one year of dating, Bush wrote that Fredinburg had remained “one of my truest friends.” “Today I find myself attempting to pick up the pieces of my heart that have broken into such tiny shards. I’ll likely never find them all. Today I, and so many of my loved ones, lost an incredible friend. Dan Fredinburg was one-of-a-kind. Fearless. Funny. A dancing robot who liked to ride dinosaurs and chase the sun and envision a better future for the world. His brain knew how to build it. His heart was constantly evolving to push himself to make it so,” Bush wrote on Saturday.

So grateful to be on the arm of the benevolent, world changing @sophiabush at the #DSAwards @DoSomething

A photo posted by Dan Fredinburg (@danfredinburg) on

“He was one of my favorite human beings on Earth. He was one of the great loves of my life. He was one of my truest friends. He was an incredible brother, a brilliant engineer, and a damn good man,” Bush continued.

Bush has continued to honor Fredinburg on social media, encouraging her followers to donate to OrphanGift, the cause he was climbing Everest for. According to the donation page, titled “Celebrating Dan,” all donations will “go directly to relief efforts and the children [affected] by the disaster.”

“He went to a place he loved to pursue his dream and find his peace, and he made sure his happiness would give happiness to others. He was raising funds for OrphanGift. We will continue doing so for him. If his story has inspired you, helped light a fire in you, or touched your heart, please consider helping us carry out his mission,” Bush wrote on Instagram, sharing a link to the Crowd Rise campaign.

Fredinburg’s sister Megan also shared a link to the campaign on Fredinburg’s Instagram, and thanked followers for their support. She also announced that she would be sharing a few photos in the coming days that her brother had asked her to post for him on Instagram while he continued his climb. “Day 23: Final day of ice training. We dressed up for Goddess Everest in our finest onsies. #Everest2015 #StayWild,” Fredinburg captioned the image below.