Melania Trump unveils stamp honoring Barbara Bush, with George W. Bush absent

First lady Melania Trump hosted the unveiling of a U.S. Postal Service stamp honoring former first lady Barbara Bush at the White House on Thursday -- with a notable absence of former President George W. Bush.

A number of family and friends of the Bush family, including Neil Bush and Dorothy Bush Koch, filled the East Room for the event honoring the former first lady, who died in 2018 at the age of 92.

Dorothy Bush Koch, the youngest child of the 41st president and first lady, spoke about her mother's impact in transforming the White House into a "true home."

Melania Trump, who has made few appearances in Washington during her husband's first three months in office, celebrated Barbara Bush's political and family life.

"Mrs. Bush's legacy is marked by her respect for tradition while also breaking with convention," Melania Trump said.

Other Bush children, George W. Bush and Jeb Bush, did not attend the event.

George W. Bush, who has kept a relatively low profile since leaving office, was in Washington for President Donald Trump's inauguration earlier this year. He was seated near former Secretary of State Hillary Clinton, former President Bill Clinton and former President Barack Obama.

But he has otherwise kept Trump, a fellow Republican, at arm's length and the two have a history of mutual criticism.

ABC News reached out to George W. Bush's office for comment on Thursday's event.

George W. Bush didn't endorse Trump in any of his presidential campaigns. In 2020, he said he didn't vote for either Trump or Joe Biden, but rather wrote in Condoleezza Rice, who served as his secretary of state between 2005 and 2009.

He and his father, late President George H.W. Bush, were critical of Trump in a 2017 book, in which they expressed concern about his impact on the Republican Party and conservative values. In a rare public speech that same year, George W. Bush condemned the brand of politics embraced by Trump and his supporters, though didn't explicitly mention Trump by name.

Barbara Bush once said of Trump, "I don't understand why people are for him."

Trump's criticism of the Bush family ramped up during the 2016 Republican presidential primary as he went after Jeb Bush as "low energy." He later bragged of beating the "Bush Dynasty" after his election victory.

Trump has also repeatedly criticized George W. Bush's response to the Sept. 11, 2001, terrorist attacks and the Iraq war.

"Bush led a failed and uninspiring presidency. He shouldn't be lecturing anybody!" Trump said in 2021 after George W. Bush gave a 20th anniversary speech in which he warned domestic terrorism posed as much of a threat as foreign terrorists.