An anti-Ted Cruz super PAC that did not have to disclose its donors before Election Day was mostly funded by a top national Democratic group, a new filing with the Federal Election Commission reveals.

The anti-Cruz super PAC, Texas Forever, popped up in the final days of the Republican U.S. senator's re-election race against U.S. Rep. Beto O'Rourke, D-El Paso, forming after the date that would have required it to report its donors before the election. The group went on to spend $2.3 million on a last-minute ad blitz against Cruz, who ended up beating O'Rourke by a small margin.

In its post-election filing Thursday with the FEC, Texas Forever said it had received $2.35 million in donations from Senate Majority PAC, the super PAC aligned with Senate Minority Leader Chuck Schumer that works to elect Democrats in the upper chamber. Texas Forever also got $10,000 from filmmaker James Brooks.

On Nov. 16, Texas Forever returned $58,000 to Senate Majority PAC, the filing shows.

Super PACs were involved on both sides of the Senate race, though Texas Forever was the only one that took advantage of the loophole allowing it to delay donor disclosure until after Election Day. The involvement of the super PACs on the Democratic side came despite O'Rourke's insistence that he did not want the help of such groups, which can raise and spend unlimited amounts of money in an election as long as they do not coordinate with candidates.