Republican presidential hopeful Jeb Bush, the former governor of Florida, will be joined by his brother, former President George W. Bush, for a 9/11 commemoration in New York City. Above, Bush addresses an economic summit hosted by Florida Gov. Rick Scott in Orlando, Florida, June 2, 2015. REUTERS/Steve Nesius

Former President George W. Bush is set to headline a fundraiser next month for his brother, former Florida Gov. Jeb Bush, on the eve of the 14th anniversary of the Sept. 11, 2001, attacks. The announcement comes as the 43rd president has become an increasingly vocal supporter of his brother's campaign.

The former president has not yet appeared publicly campaigning alongside Jeb Bush, but he has plans to join a late October donor retreat in Houston alongside their father, George H.W. Bush, and former first lady Barbara Bush, in addition to the upcoming one in New York. Other fundraising events are in the works as well, the Washington Post reported.

"It's no secret that President Bush is all in for Jeb, and he's proud to help by participating in fundraisers across the country as his schedule permits," Freddy Ford, a spokesman for George W. Bush, said in a statement.

Last week, the former president sent out an email to his supporters: "“I rarely send emails like this, but I wanted to make sure I asked for your support on behalf of my brother, Jeb.”

“My brother will be a tremendous President,” Bush wrote, in the email requesting donations for his brother's campaign. “He is a proven leader with an optimistic outlook and a clear agenda for America’s future.”

The former president has been out of politics since he left office, but his brother's run has reignited debates over his legacy, particularly in relation to the war in Iraq, which is widely considered to have been a mistake. Democrats have sought to link the former governor with his brother's policies.

Jeb Bush has said that he will act independently and differently than his brother and father. Jeb Bush currently sits in second place in national polls of GOP candidates, with 10.3 percent of the vote. Donald Trump continues to lead the Republican party with 26.1 percent support.