Democratic 2020 White House contender Julián Castro jokingly called out organizers of a presidential forum in his home state of Texas on Monday for mistakenly using a photo of his twin brother in their promotional materials.

"I will say though that the picture y'all have in your program is actually of my brother, Joaquin. Yeah, you have my brother's picture. Yeah, that's true," Julián Castro said in Houston moments after walking on stage for his appearance at the She The People Presidential Forum.

"Prove it," co-moderator Joy Reid of MSNBC responded.

"He would say that's a good thing because he's better looking than I am, but you know?" Castro replied.

Photos of the error quickly circulated on social media.

Julián Castro, 44, is a former Obama administration housing chief. Joaquin Castro, who is one minute younger than the presidential candidate, currently represents Texas' 20th Congressional District.

The pair frequently joke about getting confused for one another, a situation that was temporarily avoided earlier in 2019 when Joaquin Castro grew a beard. The congressman has since shaved off the extra facial hair.

During a CNN town hall in April, Julián Castro told host Don Lemon his brother usually quipped that the elder Castro was "a minute uglier" than him.

"No one has ever heard that joke before, right?" Lemon said, smiling.

"I know, only a million times," Castro retorted.

Castro was joined in Houston by fellow White House hopefuls Sens. Cory Booker of New Jersey, Kamala Harris of California, Amy Klobuchar of Minnesota, Bernie Sanders of Vermont, and Elizabeth Warren of Massachusetts, as well as Rep. Tulsi Gabbard of Hawaii and former congressman Beto O'Rourke of Texas.

Castro is polling at about 1.3%, according to RealClearPolitics' average.

[Also read: Julián Castro compares Trump administration to Third Reich]