Former U.N. Ambassador Nikki Haley will speak Tuesday at the Republican National Convention in what will be a highly anticipated speech by former President Donald Trump's last major challenger in this year's GOP primary, a source familiar with her decision told Spectrum News.

The decision on Sunday came one day after a gunman opened fire at Trump’s rally in Butler, Pennsylvania, in what law enforcement are investigating as an attempted assassination. Trump said the upper part of his right ear was pierced in the shooting.

Haley, who was also elected twice as South Carolina governor, was added to the schedule after she was initially not among the list of speakers, Haley spokesperson Chaney Denton told the Associated Press.

Denton had said last week that the former South Carolina governor was not invited to the convention, but Haley had instructed her delegates to vote for Trump and issued a public call for party unity.

During the primary, Haley accused Trump of causing chaos and disregarding the importance of U.S. alliances abroad. She did not endorse him when she dropped out in early March, instead waiting more than two months before she said she planned to vote for him.

Trump, in turn, repeatedly mocked her with the nickname “Birdbrain,” though he curtailed his criticism after securing enough delegates in March to become the presumptive Republican nominee.