A single billionaire provided the lion's share of the money to the main Republican super-PAC set up to destroy Donald Trump Donald John TrumpREAD: Cohen testimony alleges Trump knew Stone talked with WikiLeaks about DNC emails Trump urges North Korea to denuclearize ahead of summit Venezuela's Maduro says he fears 'bad' people around Trump MORE.

Marlene Ricketts, the matriarch of the Ricketts family that owns the Chicago Cubs baseball team, contributed $3 million to the anti-Trump super-PAC "Our Principles PAC," which is being run by former Mitt Romney adviser Katie Packer.

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The super-PAC has spent more than $4 million running attack ads against the GOP front-runner in Iowa, New Hampshire, and South Carolina. It is the only serious anti-Trump group to date in a campaign cycle in which Republicans have been reluctant to take on their front-runner.

Until now, the identities of the donors funding Our Principles PAC had been kept secret, fueling the rumor mill in Washington. But the Federal Election Commission reveals that almost all the money came from Ricketts. The donor's identity was first reported by The New York Times.

Ricketts's family had previously given $5 million to a super-PAC supporting the failed presidential bid of Scott Walker. The family is yet to swing its full weight behind another presidential candidate but clearly likes both Ted Cruz Rafael (Ted) Edward CruzCornyn less popular than Cruz in Texas: poll Trump unleashing digital juggernaut ahead of 2020 Inviting Kim Jong Un to Washington MORE and Marco Rubio Marco Antonio RubioWhite House pleads with Senate GOP on emergency declaration Sixteen years later, let's finally heed the call of the 9/11 Commission Schumer urges GOP to reject Trump's 'destructive' national emergency MORE. In June last year, Marlene Ricketts gave $10,000 to super-PACs supporting Rubio and Cruz.

Besides a token $250 donation, the only other donor to the anti-Trump super-PAC in January was Illinois businessman Richard Uihlein, who gave just $7,500.

Uihlein had previously given $2.5 million to Walker's super-PAC, but after the Wisconsin governor quit the race he shifted to the Cruz camp and recently gave $1 million to a pro-Cruz super-PAC.