The Instagram account for Bush's service dog, Sully, posted a touching photo of the dog in front of Bush's casket with the caption "Mission complete" following the 41st president's death at 94 on Friday.
Sully is staying by Bush's side as the family prepares for his funeral on Thursday at his presidential library in College Station, Texas.
Bush introduced Sully in June by releasing a photo of himself sitting with the yellow Labrador and a special guest, former president Bill Clinton.
Sully was sent to Bush by America's VetDogs, an organization that trains and places service dogs with disabled military veterans and first responders. Bush was a pilot in the Navy who served in World War II.
Sully is named after Chesley "Sully" Sullenberger, the former pilot who famously landed his disabled plane in New York's Hudson River in 2009 to save the lives of 155 people. Even before he arrived at his new home with Bush, Sully had his own Instagram page.
He became such a beloved part of Bush's life that Bush even had socks with Sully's face on them as part of his colorful sock collection.
After helping Bush around the house with tasks like opening doors, summoning assistance and picking up dropped items, Sully will now have a new mission.
He will be joining the Walter Reed National Military Medical Center's Facility Dog Program after the holidays, America's VetDogs announced.
"(Sully) will be working alongside fellow VetDogs facility dogs SGT Dillon and SGT Truman who are there to assist with physical and occupational therapy to wounded soldiers and active duty personnel during their journey to recovery at Walter Reed Bethesda,'' the organization wrote on Facebook.
The group of six facility dogs at Walter Reed average 2,500 contacts and more than 200 working hours per month to help wounded and active duty soldiers, according to the hospital.
"As much as our family is going to miss this dog, we're comforted to know he'll bring the same joy to his new home, Walter Reed, that he brought to 41," Bush's son, former president George W. Bush, wrote on Instagram.