San Antonio Mayor Julián Castro, who was jokingly mistaken for a White House intern by Barack Obama less than three years ago, will deliver the keynote address at the Democratic National Convention that will nominate the president for a second term.

Castro will speak in prime time on Sept. 4, the first night of the convention in Charlotte, N.C. First lady Michelle Obama is scheduled to deliver remarks the same night.

The appearance, announced this morning in a video released to the television network Univision, puts Castro in the company of Texas Democrats like Gov. Ann Richards, who was state treasurer when she delivered her keynote in 1988, and Congresswoman Barbara Jordan, who was awarded the prime speaking role in 1976 and 1992.

Obama is a past keynote speaker as well: In 2004, as a state senator from Illinois, he was thrust into the national spotlight, setting the stage for his ascendancy to the White House.

Castro, whose famous first encounter with Obama occurred during a roundtable discussion on green jobs in 2009, sat in the first lady's box during the president's State of the Union address earlier this year.

The 37-year-old, now in his second term as mayor of the state's second-largest and the nation's seventh-largest city, delivered the keynote speech at the Texas Democratic Party’s convention last month in Houston. He is widely considered a future candidate for statewide or federal office, though he recently said he'll keep his current job through 2017 "if the voters have [him]."

The decision to entrust Castro with the keynote comes in a year when many analysts believe turnout among Hispanics could be the deciding factor in the general election contest between Obama and Republican nominee Mitt Romney.

The National Association of Latino Elected and Appointed Officials estimates that 12.2 million Hispanics will vote in the presidential race, up from 9.7 million in 2008. Although Texas is almost certain to vote Republican in November, the Hispanic vote could be key in several swing states, including Florida, Colorado and New Mexico.

Castro and his brother, state Rep. Joaquin Castro, D-San Antonio, are the twin sons of Rosie Castro, a community activist in San Antonio and a former leader of the La Raza Unida movement.

Born on Mexican Independence Day, the brothers earned undergraduate degrees with honors from Stanford University and law degrees from Harvard University.

In 2001, Julián Castro became, at 26, the youngest City Council member in San Antonio’s history. In 2005, he ran for mayor, narrowly losing a runoff to Phil Hardberger, the former chief justice of the 4th Court of Appeals.

Castro ran again in 2009 and won, becoming the youngest mayor of a major American city. He was re-elected in 2011 with 82 percent of the vote.