Read President George H.W. Bush's Letter to Trump on Why He'll Miss the Inauguration

The Obamas, Clintons, and former Presidents George W. Bush and Jimmy Carter are all expected to attend Trump's inauguration on Jan. 20, but one living former president will be notably absent. George H.W. Bush and former First Lady Barbara Bush will not attend the ceremony after both being hospitalized in recent days.

According to a statement released by a spokesman, Jim McGrath, George H.W. Bush was admitted to Houston Methodist Hospital over the weekend to treat pneumonia and underwent a procedure to clear his airway. He is now stable in the intensive care unit. Former First Lady Barbara Bush was admitted to the hospital on the morning of Jan. 18 as a precautionary measure after experiencing fatigue and a cough.

Even before his hospitalization, George H.W. Bush let the president-elect know that he would be unable to attend his swearing in. In a letter, shared by ABC News, the former President wrote that, according to his doctor, attending would likely put him "six feet under." He went on to write that he and Barbara would be with Trump — and the country — in spirit, and wished the president elect the very best.

George H.W. Bush sent letter to Trump on Jan. 10 stating he couldn't attend Inauguration: "We will be with you and the country in spirit." pic.twitter.com/zcoieQJmP6

— ABC News (@ABC) January 18, 2017

Despite Bush's well wishes and the expected attendance of former presidents and first ladies, more than 50 lawmakers have made the decision to boycott Trump's inauguration following his critical comments last week about Rep. John Lewis, a prominent civil-rights icon.