For those of us who were waiting to hear about Julian Castro's next move, the news was quick in coming.

The former secretary of housing and the only Latino candidate in the Democratic nomination race announced that he would endorse Sen. Elizabeth Warren, only days after the end of his own campaign.

In a message posted on Twitter on Monday, Castro said he was proud to support Warren in her race for the presidency.

"Elizabeth and I share a vision of America where everyone counts," he said. "An America where people – not the wealthy or well-connected – are put first. I'm proud to join her in fighting for big, structural change.”

Castro's support comes at a key time for Warren’s career, since she has lagged in the polls in recent weeks, following closely behind Vermont Senator Bernie Sanders and former Vice President Joe Biden.

While Sanders has the support of another heavyweight Latino in national politics, Bronx Rep. Alexandria Ocasio-Cortez, Castro's endorsement of Warren could represent a major shift in the outline of the Democratic primary.

"There is one candidate I see who is unafraid to fight like hell to make sure that America’s promise will be there for everyone,” Castro said in a video accompanying his announcement. "She will make sure that no matter where you live in America – or where your family comes from in the world, you have a path to opportunity, too.”

For her part, the Massachusetts Senator thanked her former opponent for his support, saying she felt honored by his endorsement.

"Together, we’ll fight to make sure every single family in America has a path to opportunity," she added in a Twitter message.