Democratic Sen. Ruben Diaz, Sr. endorsed Republican candidate for governor Rob Astorino on Thursday and called on Gov. Andrew Cuomo to debate him on TV one-on-one.

“This is the right thing to do,” Diaz said at a joint appearance with Astorino and his running mate, Chris Moss, in the Bronx.

Diaz is a Bronx Democrat who holds deeply conservative views on abortion and same-sex marriage.

He is also considered an unpredictable maverick and has openly criticized Cuomo in the past for endorsing Republican candidates (Two of whom backed the legalization of same-sex marriage in 2011).

Diaz today knocked Cuomo for lacking clarity on whether he supports the Dream Act (Cuomo says he does), which would provide tuition assistance to undocumented immigrants.

Astorino backs an alternative method, known as the Dream Fund, which uses private funds rather than public dollars — a proposal that Hispanic lawmakers backing the Dream Act say is insufficient.

Diaz’s son, Bronx Borough President Ruben Diaz, Jr., was early on tapped as a co-chair of Cuomo’s re-election campaign.

Astorino’s backing from Diaz Sr. comes as he seeks to reach out to Hispanic and black voters — a formula that’s worked for him in his campaigns for county executive in 2009 and 2013.

Cuomo last month sought to court Diaz, a Pentecostal minister, by breaking bread with him at lunch.

In a release signed by groups that endorsed Cuomo, including NARAL Pro-Choice New York and the Empire State Pride Agenda, Diaz was called “ultraconservative, anti-choice, homophobic.”

β€œIt’s becoming abundantly clear why ultraconservative Republican Rob Astorino is trailing in the polls and refusing to debate the Governor one-on-one. By standing with one of the most strident anti-choice, anti-women homophobic zealots in the state of New York, Astorino has shown his true colors. This is a pro-choice, pro-equality state, and Rob Astorino is completely out of step with mainstream New Yorkers. We are united in opposition to Astorino and will do everything in our power to ensure he is soundly defeated.”

A similar blast was leveled against Astorino when he received the backing of Texas Gov. Rick Perry.