Bernie Sanders will endorse Hillary Clinton for president at an event Tuesday that will be in New Hampshire, a source intimately involved in Clinton campaign field operations and strategy confirmed to CBS News on Thursday.

The source confirmed to CBS News' Major Garrett that advance teams are preparing for the dual event.

Clinton's campaign, the source added, is also coordinating planning with the Democratic National Committee to maximize the impact of a Sanders endorsement and to demonstrate party unity ahead of the Republican National Convention the week after next.

Sanders came very close to officially endorsing her in an interview Thursday with Bloomberg's Al Hunt.

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"We have got to do everything that we can to defeat Donald Trump and elect Hillary Clinton," he said in an interview that will air on PBS's "Charlie Rose" program. "I don't honestly know how we would survive four years of a Donald Trump" as president.

While he still hasn't officially dropped out of the presidential race, late last month, Sanders had also said that he will vote for Clinton in November's general election.

The endorsement will come after a long primary battle between Sanders and Clinton during which they each went after each other's policy positions and voting records. Sanders even questioned whether Clinton was qualified to be commander-in-chief at one point, although he quickly walked the statement back.

While Clinton endorsed then-Senator Obama just a few days after the end of the presidential primary cycle in 2008, Sanders has waited much longer since the primaries officially ended in mid-June to make a move.

Sanders is trying to influence changes in the Democratic Party platform this month, though Clinton has already proposed an expansion in her college affordability plan.

The endorsement will come a few weeks before they head to their convention in Philadelphia at the end of the month.