GOP mega-donor Wall Street billionaire Paul Singer is actively fundraising for Sen. Marco Rubio (R-FL), several sources have confirmed for Breitbart News.

One, a source close to Rubio and Rubio’s presidential campaign, confirmed it to Breitbart News’ Sarah Rumpf—who is in Miami at Rubio’s campaign rollout. Others, including sources close to Singer, have also confirmed it to Breitbart News.

Singer himself is worth about $2 billion and runs the hedge fund Elliott Management Corporation. Singer donated $1 million to the Super PAC Restore Our Future in 2011 to help Mitt Romney win the GOP nomination, and has donated to several major causes, candidates and groups over the years. He also helped George W. Bush’s presidential efforts, and pushed Rudy Giuliani in the 2008 election.

Singer helping Rubio is a coup in the quest for donors among 2016 candidates, as Singer is known for being extraordinarily active in terms of pushing his wealthy friends to also support the candidates and causes he does.

Rubio’s presidential campaign announcement comes one day after former Secretary of State Hillary Clinton announced she is running for the Democratic nomination, and makes him the third Republican in the race after Sens. Ted Cruz (R-TX) and Rand Paul (R-KY) announced their candidacies in recent weeks.

Sarah Rumpf contributed reporting from Miami