The labrador who worked as a service dog for President George HW Bush has been pictured resting beside his coffin, in a moving tribute.
Mr Bush, who served as the 41st US president between 1989 and 1993, died late on Friday at the age of 94.
Sully the dog is travelling with the casket on the flight from Texas to Washington and back this week.
Mr Bush's body is due to lie in state this week ahead of a day of national mourning.
The coffin is being flown from Texas to DC on board Air Force One - temporarily renamed Special Air Mission 41, in homage to the late president - and then back on Wednesday, with Sully accompanying the body throughout.
The picture was tweeted by Mr Bush's spokesman, Jim McGrath, showing Sully next to Mr Bush's casket on Sunday along with the caption: "Mission complete."
Social media users thanked Sully for his services and commented on his and dogs' loyalty generally towards their owners.
Loyal until the end. Why we love dogs so much. R.I.P. #Remembering41— Mayra SGdT (@SamSofiMama) December 3, 2018
OMG 😭 - we don't deserve dogs, they are just the best, what a tremendously loyal and loving pooch and glad that he could help make Bush 41's final months a little easier - Well done, Sully. 🐶#Remembering41— Phillydude 41-33 (@Fairwinds10) December 3, 2018
Sully is named after the airline pilot Chesley "Sully" Sullenberger, who landed a passenger jet on the Hudson River in 2009, saving all 155 passengers and crew on board.
The two-year-old labrador was assigned earlier this year as a service dog to Mr Bush who used a wheelchair in the last years of his life.
A great joy to welcome home the newest member of our family, "Sully," a beautiful -- and beautifully trained -- lab from @AmericasVetDogs. Could not be more grateful, especially for their commitment to our veterans. pic.twitter.com/Fx4ZCZAJT8— George Bush (@GeorgeHWBush) June 25, 2018
A highly trained dog, Sully can perform a number of commands, including opening doors and fetching items such as the phone when it rings.
He will now work as a service dog, assisting with therapy for wounded soldiers.
Sully has his own Instagram account; here he is shown "assisting with voting" as Mr Bush cast his ballot in last month's US presidential mid-term election.
View this post on Instagram
Assisting with voting must be easier with thumbs. It was very nice of Secretary James Baker to help my best friend cast his vote. They didn’t even let me push the button! . . #vote . . . . . . #SullyHWBush #SullyBush #bush41 #instagood #goodboy #DogOfInstagram #TalesOfALab #InstaDog #InstaDogs #Dogs #AmericasVetDogs #GuidedogFoundation #labrador
Not all US presidents have been fond of dogs, though: John F Kennedy was allergic to dogs, and Donald Trump does not have one.
President Bush had been receiving treatment for a form of Parkinson's disease and had been admitted to hospital with a blood infection in April.
He died in Houston, Texas.
He will be buried at the presidential library in Texas, alongside his wife of more than 70 years, Barbara Bush, who died seven months ago.