U.S. Rep. Joaquín Castro (D-San Antonio) said his twin brother Julián Castro (left) is running for president. Credit: Marjorie Kamys Cotera / Texas Tribune

In case there was any mystery left, Julián Castro is running for president.

That’s according to his twin brother, U.S. Rep. Joaquin Castro (D-Texas), who made the announcement during a joint interview Thursday night on CBS’s “The Late Show with Stephen Colbert.” As Colbert teased Julián Castro about the build-up to his all-but-certain 2020 campaign, Joaquín Castro interjected.

“I’ll speak on his behalf here,” Joaquin Castro said. “He’s gonna run for president. How about that?”

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The comment drew a grin and nod from Julián Castro, the former U.S. housing secretary and San Antonio mayor.

He announced Wednesday that he was forming a presidential exploratory committee and would make an announcement Jan. 12 in San Antonio. For months, however, he has hardly concealed his ambitions, releasing a book, visiting early voting states and even saying in recent weeks that he is “very likely” to run.

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Patrick Svitek, The Texas Tribune

Patrick Svitek is the primary political correspondent for The Texas Tribune and editor of The Blast, the Tribune's subscription-only daily newsletter for political insiders.