Kansas Gov. Sam Brownback will endorse Texas Gov. Rick Perry as the Republican nominee for president in Florida Thursday, a source close to the Perry campaign confirmed to ABC News.

Brownback, who will be the first former presidential candidate to endorse the governor, will attend a Fox News debate as Perry’s guest.

Brownback is the third governor to lend his support to the Perry campaign. Last week, Louisiana Gov. Bobby Jindal accompanied Perry to the CNN debate in Tampa, Fla., and announced his support for the Texas governor, and one day later, Nevada Gov. Brian Sandoval endorsed Perry as well.

Brownback, who once served as a U.S. senator espousing social conservative causes, was the lone governor to attend Perry’s day of prayer and fasting in Houston in early August.

Brownback’s support will add to the bevy of endorsements rolled out by the Perry campaign this week. On Wednesday, Perry’s campaign announced the support of 27 state legislators in New Hampshire and 21 state assembly members in South Carolina, along with snagging a former Romney supporter, Van Poole, the former chairman of the Republican Party of Florida and co-chairman of Mitt Romney’s steering committee in Florida in 2008.