Former Housing and Urban Development Secretary Julián Castro on Monday endorsed Sen. Elizabeth Warren Elizabeth WarrenNo new taxes for the ultra rich — fix bad tax policy instead Democrats back away from quick reversal of Trump tax cuts It's time for newspapers to stop endorsing presidential candidates MORE (D-Mass.) in the 2020 Democratic presidential primary.

The move arrives less than a week after Castro announced he was dropping out of the presidential race after failing to gain momentum in the crowded Democratic field.

The endorsement by Castro, who was the only Latino candidate in the presidential race and made immigration reform a cornerstone of his campaign, comes as 2020 Democrats look to gain support among Latino voters ahead of the coming election.

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Castro announced the endorsement in a tweet, sharing a video and saying he was “proud” to endorse Warren “in her fight for big, structural change.”

Today I'm proud to endorse @ewarren for president.



Elizabeth and I share a vision of America where everyone counts. An America where people⁠—not the wealthy or well-connected⁠—are put first. I'm proud to join her in the fight for big, structural change. pic.twitter.com/xDvMEKqpF3 — Julián Castro (@JulianCastro) January 6, 2020

Following the announcement, the Warren campaign revealed it would be traveling to New York on Tuesday to hold a special event with Castro at Kings Theatre in Brooklyn.

Though Castro butted heads several times with Democratic candidates such as former Vice President Joe Biden Joe BidenThe Memo: Warning signs flash for Trump on debates Senate Republicans signal openness to working with Biden National postal mail handlers union endorses Biden MORE and former Rep. Beto O'Rourke Beto O'RourkeJimmy Carter says his son smoked pot with Willie Nelson on White House roof O'Rourke endorses Kennedy for Senate: 'A champion for the values we're most proud of' 2020 Democrats do convention Zoom call MORE (Texas) during his yearlong campaign, his interactions with Warren were noticeably warmer throughout the race.

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On multiple occasions during her campaign, Warren, whom polls have placed as a leading Democratic presidential contender for much of the race, has offered praise to Castro for his progressive positions on issues like immigration.

When pressed during an interview last May about the best policy idea she had heard from one of her opponents, Warren pointed to Castro’s immigration plan.

“Oh, I think Julián Castro. His idea around immigration and about changing how we treat people who come here and who are not documented,” she said. “I think he’s got some really good ideas around this. I am very interested in his work. I admire it.”

She also name-dropped Castro a month later when she joined his call to decriminalize illegal border crossings.

“I agree with Secretary Castro,” Warren told HuffPost then. “We should not be criminalizing mamas and babies trying to flee violence at home or trying to build a better future. We must pass comprehensive immigration reform that is in line with our values, creates a pathway to citizenship for undocumented immigrants including our DREAMers, and protects our borders.”

In response, Castro thanked Warren on Twitter.

She also gave a shoutout to Castro last October after she said she would be joining the then-fellow Democratic candidate in opposing a proposed measure in Las Vegas that sought to criminalize homelessness.

That announcement earned Warren applause from Sawyer Hackett, Castro's national press secretary at the time, who called her a “true class act" for mentioning Castro by name.

“Every candidate should speak out against an ordinance that criminalizes desperation and those experiencing homelessness. Shoutout to @ewarren for once again giving props to @JulianCastro by name—a true class act,” Hackett wrote.

Updated at 9:48 a.m.