Donald Trump is keeping the birther movement alive and has taken aim at Canadian born Sen. Ted Cruz (R-Texas).

Cruz announced on Monday that he will run for president and Trump, who is also considering a presidential bid, wondered if the Texan was even eligible to become commander-in-chief.

"It's a hurdle, somebody could certainly look at it very seriously," Trump told My Fox New York on Monday, about Cruz's foreign birthplace.

The senator was born in Alberta to an American mother and a Cuban born father. Cruz's Canadian roots have caused some questions about his presidential bid, though many experts say they don't affect his eligibility due to his mother's citizenship.

"He was born in Canada. If you know and when we all studied our history lessons, you are supposed to be born in this country, so I just don't know how the courts would rule on it. It's an additional hurdle that he has," Trump added, hinting that Cruz wouldn't qualify as a "natural born citizen," one of the constitutional requirements for a U.S. president.

Trump, who was born in Queens, New York, previously spearheaded the effort to question the legitimacy of President Barack Obama's birth certificate and alleged Obama was actually born abroad and forged the document to list Hawaii as his birthplace.

The White House ultimately released Obama's birth certificate in 2011 after the president complained "this thing just keeps on going."

Though Trump voiced his doubts about Cruz's birthplace, the real estate reality star did compliment Cruz's chances.

"It's going to be interesting to see how Ted does. I know him very well, he's a smart guy and could do pretty well. It's not going to easy for anybody, it's going to be a competitive field," Trump told the morning show.

Earlier this month, Trump said that he is forming an exploratory committee to consider a presidential run and bragged, "I get the biggest crowds," when asked about events he held in New Hampshire.

"I'll decide sometime by June," he said about the timeline for a potential campaign announcement.