Photo of George H.W. Bush's service dog mourning at his casket pulls the internet's heartstrings

Sully HW Bush/Instagram

Sully in front of George HW Bush's casket on Sunday.

• A photo posted of George H.W. Bush's service dog mourning beside the casket of his old master has left social media a little teary-eyed
• The heartfelt photo, posted initially by H.W.'s son and 43rd US president, George, shows the yellow lab slumped by Bush's casket.
• Sully is to make his final journey with his old companion to Washington, DC, on Monday, a report says.
• The 41st US president will lie in state there from Monday to Wednesday.
• Bush died at the age of 94 on Friday. He was president from 1989 to 1993.

A photo of George HW Bush's service dog lying downbeat besides the casket of his old master on Sunday has spread across social media, causing an outpouring of emotion.

Bush's son Jeb, Governor of Florida, retweeted the photo, with the simple words: "Sully has the watch."

Abigail Ogle, KOCO News anchor, tweeted: "Sully, the service dog of President George H.W. Bush, keeping watch over his best friend. Rest In Peace, 41. Good boy, Sully."

X-Men actress Olivia Munn shared the photo, saying: "This is his pup Sully, lying beside him til the very end. Thank you for your service, Mr. President."

Fox News host Bret Baier tweeted: "That is just a great pic of Sully the service dog who served @GeorgeHWBush Wow."

Sully will reportedly make one last journey with the former president, accompanying his casket to Washington, DC, where Bush will lie in state from Monday.

The yellow Labrador Sully started serving as Bush's companion in June - after Bush's wife and passed away in April.

Sully will now make the final journey with Bush's casket to Washington, DC, on Monday afternoon a source told CNN, where the 41st president will lie in state at the US Capitol from 5 p.m. on Monday until 10 a.m. on Wednesday.

Before that his remains will be taken to Ellington Field Joint Reserve Base, Houston and Joint Base Andrews, Maryland, ABC said.

His son and 43rd US president George W Bush posted an Instagram photo of Sully lying in front of his old master's casket on Sunday.

Read more: PHOTOS: The life and legacy of George HW Bush

Bush wrote: "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 be brought to 41."

Sully is to return to the Walter Reed National Military Medical Center, where he will help other people in the future.

The service dog Sully is named after the famous US Airways pilot who safely landed a passenger plane on New York's Hudson River in 2009.  

Bush Senior died at on Friday at the age of 94. He suffered from a form of Parkinson's disease and was hospitalized periodically in recent years for pneumonia.