
The Secret Service agents who protected Barbara Bush for two decades after she left the White House have been standing guard over her coffin, refusing to the leave the side of the woman they say treated them like family.

The agents swapped out at St. Martin's Episcopal Church in Houston, Texas, taking turns on Friday as mourners came in their droves to pay their respects to the former First Lady.

They stood in the background as fans greeted former president George H.W. Bush in his wheelchair, giving a final act of protection to the 92-year-old.

One former agent said they were proud to stand by her side one final time.

'Agents on her detail, they're the ones posted around her house all of the time. They're the ones who bring her shopping. They're the ones who bring her to events. They are family to her.

'She was one of the most gracious people we've ever protected.

Secret Service Agents stand guard at St Martin's Episcopal Church in Houston, Texas, on April 20 next to former First Lady Barbara Bush's coffin

'She went out of her way to make us feel like part of the Bush family. It was just a wonderful relationship we had,' former agent Thom Bolsch told ABC 13.

John Lopez, a local reporter who was at the church, said they were 'refusing' to leave.

'Barbara Bush's Secret Service detail, several of whom have been been with her for decades, refuse to leave her side until she is buried. Very powerful,' he tweeted.

Barbara's code name was 'Tranquility' which Secret Service agents said could not have been more fitting.

In a touching tribute to the former First Lady on Friday, written by former agent Jonathan Wackrow for CNN, he said of the name: 'It exemplified her demeanor and its calming, humanizing and gentle effect on those around her.

'She will be forever missed.'

Wackrow nostalgically described two heartwarming moments with Barbara which he said inspired him to continue to serve the 'sacred institution' of the First Lady for years to come.

The agents stayed as the mourners came to pay their respects on Friday before Saturday's funeral

The agents swapped around and took turns watching over her casket. Some have protected her for decades and say she treated them like family

George H.W. Bush stood with his daughter Dorothy at the foot of his wife's casket on Friday then greeted hundreds of mourners who had come to pay their respects

The first was when he had just finished an overnight shift at the Bush summer residence in Maine.

'In my world, it was better to be unseen, but in this instant, I was in the former first lady's full view with nowhere to hide.

'Mrs. Bush gave me the warmest smile and said, "Well, it is good morning for me, but it looks like you have been up all night, so I will wish you a good night's sleep." Stunned, I thanked her.'

The second was after she had left the White House and during a trip to New Jersey.

Once they had exited New York City and were in the Garden State, a large, loud, siren-screaming police escort joined their unassuming motorcade.

Wackrow wrote: 'Typically, this was not the way that the former first lady liked to travel, as it drew undue attention. However, in this instance -- with her husband's presidency behind her -- she was thrilled.

'She treated us like part of the Bush family': Agents admired former First Lady Barbara and said they appreciated her personable approach to their work. She is pictured being escorted by two agents in 1992 as she attended Palm Sunday services at the church where her funeral was held

In a cheerful photograph taken in the White House in 1989, a Secret Service agent walks to the side of the then First Lady as she leads her springer spaniel Millie

A Secret Service agent watches over the former First Lady as she is greeted by her son, then President George W. Bush, in 2005

'Taking a quick glance in the rear-view mirror, I could see an amazing smile illuminating her face as she turned to her staff in the back seat, exclaiming, "They remember me! We have not had this much excitement since the White House!"

Before going back to New York City, he explained, Barbara got out of the car to thank all of the officers for giving her 'such a warm welcome to New Jersey'.

'I will never forget the image of Mrs. Bush shaking hands with the officers.

'It was a genuine moment of sincerity and unguarded kindness delivered out of the public eye, which, to me, defined this great woman,' he said.

The funeral of Barbara Bush was a small and private affair, with the ceremony at St. Martin's Episcopal Church in Houston.

Political pal: Karl Rove arrives at St. Martin's Episcopal Church for a funeral service

Paying tribute: Congresswoman Gabi Giffords and her husband, retired astronaut Mark Kelly

Farewell to a first lady: The funeral of Barbara Bush was held at St. Martin's Episcopal Church in Houston on Saturday morning

The Enforcer: There were three eulogies delivered during the service, one from friend Susan Baker, one from presidential historian Jon Meacham and one from Jeb Bush

Final resting place: A short while later, Mrs Bush was buried on the grounds of the George H.W. Bush Library and Museum at Texas A&M University

Preparations: Flowers are wheeled into St. Martin's Episcopal church for the funeral

Among those in attendance with be her husband of 73 years and the 41st president of the United States George H. W. Bush, her oldest son and the 43rd president of the United States George W. Bush and current first lady Melania Trump.

Three eulogies were delivered during the service from Mrs. Bush's close friend Susan Baker, presidential historian Jon Meacham and her son and formerFlorida governor Jeb Bush.

A short while later, Mrs Bush was buried on the grounds of the George H.W. Bush Library and Museum at Texas A&M University in College Station.

There she will join her daughter Robin who died at the age of 3 in 1953 from leukemia.

At least four the six living presidents will attend the funeral as in addition to the two former Bush presidents Bill Clinton and Barack Obama will also attend the service.

Mourners: At least four the six living presidents will attend the funeral as in addition to the two former Bush presidents Bill Clinton and Barack Obama will also attend the service

Former president Jimmy Carter and his wife Rosalyn will not be in attendance, with the couple's spokesperson releasing a statement saying: 'President Carter will be on a private trip overseas, and although she is recovering, Mrs. Carter is not yet able to travel following her recent intestinal surgery.'

President Trump will also not be attending the mass in order to 'avoid disruptions due to added security.'

This is not at all uncommon for a sitting president, with Obama opting not to attend the funerals of both Nancy Reagan and Betty Ford. Mrs Bush's son was not at the funeral for Lady Bird Johnson in 2007 when he was president.

Former first ladies Michelle Obama, Laura Bush and Hillary Clinton will also attend, along with past first daughters Chelsea Clinton and Mrs Bush's granddaughters Barbara Bush and Jenna Bush Hager.

The ceremony is invite only, with 1500 guests scheduled to attend.