Story highlights Donald Trump again threatened to sue Ted Cruz over whether he's eligible to run for president

The billionaire businessman and the Texas senator have been fighting in South Carolina, where they both hope to win in Saturday's primary

(CNN) Donald Trump said Tuesday he is "very seriously" thinking about filing a suit to challenge Ted Cruz's eligibility to be president.

Trump's threat of litigation, which the billionaire businessman has recently brought up several times in recent days, came during an interview on ABC's "Good Morning America" on Tuesday, when he was pressed by host George Stephanopoulos over whether he would follow through with the suit against Canada-born Cruz's presidential qualifications, as Trump has suggested he might.

Trump replied, "I'm thinking about it very seriously George, I already have a lawyer, we're looking at it very seriously, we're thinking about it."

"He was born in Canada, lived there for years, and then under that period ... you know, you take a look at this," Trump said, adding later, "When you talk about a natural born citizen, according to many great lawyers, I've been looking at very strongly over the last week."

The threat to sue came amid a flurry of attacks on the Texas senator, who has thus far mounted the most serious primary challenge to the current GOP front-runner, and whom Trump continued to accuse of dirty campaigning and lying about his positions on the Second Amendment and Obamacare.

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