Story highlights President Obama will announce his plan to nominate Julian Castro as HUD secretary

The announcement is expected Friday afternoon, a source says

Castro is the mayor of San Antonio

If confirmed for the job, Castro replaces Shaun Donovan

President Barack Obama will announce plans Friday to nominate San Antonio Mayor Julian Castro to be his next secretary of Housing and Urban Development, a government source said.

The 39-year old, three-term mayor first gained national recognition when he delivered the keynote address at the 2012 Democratic National Convention -- the first Hispanic to do so.

First elected in 2009 and re-elected in 2011 and 2013, Castro is the youngest mayor of a major American city. He has been widely considered a rising leader in the Democratic Party and some even say a potential vice presidential candidate in 2016.

Castro would replace Shaun Donovan, who the President plans to nominate as director of the Office of Management and Budget, the source said. Donovan has been a member of the Obama administration from the start.

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Both men will join Obama at the White House for the announcement Friday afternoon, the source said.

A graduate of Stanford University and Harvard Law School, Castro began his political career at a young age. At 26, he was the youngest councilman ever elected in San Antonio.

Four years later, he ran for mayor, but lost to retired judge and fellow Democrat Phil Hardberger. Another four years and Castro was in City Hall at the ripe old age of 34.

Castro was re-elected in 2011 with 82% of the vote and in 2013 with 67%.

He has spoken out in favor of same-sex marriage and of affirmative action, even telling The New York Times that it helped him get into Stanford.

Former San Antonio mayor and HUD secretary Henry Cisneros told CNN in a previous interview that Castro is a good fit for the job, noting the current mayor's record of expanding pre-K education, revitalizing San Antonio's downtown and shoring up the city's finances.

With an eye on 2016, Cisneros said the mayor could "learn the country" as HUD secretary, arguing, "It's a lot more likely he can get on that ticket from a national office than from a mayor's job."

Not everyone is a fan, though.

"He's a tax-and-spend liberal. He does not represent all Hispanics; we're not all the same," George Rodriguez, president of the tea party in San Antonio, said in 2012.

Castro is the grandson of Mexican immigrants. His grandmother came to Texas from Mexico as an orphan at the age of 6. She taught herself to read and write in Spanish, eventually finding work in San Antonio as a maid and a cook.

His twin brother Joaquin Castro, who introduced him at the DNC in 2012, represents Texas' 20th district, which includes parts of San Antonio, in the House of Representatives.