The golden Labrador, who has worked as a service dog for President George HW Bush, was resting in a moving tribute beside his casket.
Bush, who was the 41
Sully, the dog will be traveling with the casket on a flight from Texas to Washington DC on Monday.
The body of Mr. Bush will lie national mourning next week in Washington state a week ago.
The coffin is flown aboard Air Force One from Texas to DC – temporarily renamed Special Air Mission 41 in homage to the deceased president – and then back on Wednesday, with Sully accompanying the corpse throughout.
The picture was tweeted by Mr. Bush's spokesman Jim McGrath, and shows Sully beside Mr. Bush's casket on Sunday along with the inscription: "Mission complete."
. Social media users thanked Sully Services and commented on the loyalty of him and his dogs to their owners.
a passenger plane on the Hudson River in 2009, all 155 passengers and the crew on board rescued.
The two-year-old Labrador was assigned to Bush earlier this year as a companion dog to Bush, who used a wheelchair in recent years.
Sully is a well trained dog and can execute a series of commands, including answering the phone and retrieving items.
He will now work as a companion dog, assistant in treating wounded soldiers.
Sully has his own Instagram account; Here he is shown how he helps with the vote when Mr Bush voted in the US presidential election last month.
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President Bush was treated for a form of Parkinson's disease and hospitalized in April with a blood infection.
He died at the age of 94 in Houston, Texas.
He is buried with his wife Barbara Bush, who died seven months ago, in the Presidential Library in Texas.