The father of the man who shot and killed 49 people at a gay nightclub in Orlando, Fla., was seated directly behind Hillary Clinton during a campaign rally Monday evening in the Sunshine State.

"The rally was a 3,000-person, open-door event for the public," a Clinton campaign source told the Washington Examiner. "This individual wasn't invited as a guest and the campaign was unaware of his attendance until after the event."

Clinton appeared in Kissimmee Monday to talk about jobs and the economy, but she began the rally with a tribute to the victims of the Pulse Nightclub massacre.

"I know how many people, families, loved ones and friends are still grieving, and we will be with you as you rebuild your lives, as you rebuild hope for the future," she said, "because we can't ever let that kind of hatred and violence break the spirit, break the soul of any place in America!"

Omar Mateen, 30, entered the Pulse Nightclub in Orlando early in the morning on June 12 armed with handguns and an AR-15-style rifle, murdered 49 patrons and wounded 53 more.

He was later killed by law enforcement agents.

As Clinton spoke Monday in honor of the victims of the nightclub shooting, a local NBC News affiliate spotted Mateen's father, Seddique, seated directly behind the Democratic presidential candidate.

WPTV stopped Mateen immediately after the rally and asked him about his attendance, to which he would only respond, "We've been cooperating with the federal government, and that's about it. Thank you."

However, he later opened up to the local news group, and told them a little more about his decision to go to the rally.

"Hillary Clinton is good for United States versus Donald Trump, who has no solutions," he said, revealing he had even brought a homemade pro-Clinton sign.

Asked about sitting directly behind the candidate, and whether he knew if her campaign was aware, Mateen said, "It's a Democratic party, so everyone can join."

His final remarks came in response to being asked if he thought anyone would be surprised to see him at the rally. He answered that question by saying, "Why should they be surprised? I love the United States, and I've been living here a long time."

Mateen's presence is doubly notable given Clinton also spoke out against gun violence and the gun lobby, promising her supporters Monday that she would bring both issues under control as president.

"Yes, we are going after the gun lobby, and try to get common sense gun-safety measures" she said.

"Here's what I want you to know. We are not going to repeal the Second Amendment. We are not going to take anybody's gun away," she added. "We are going to try to prevent somebody who shouldn't have a gun from shooting you or someone you care about."

A spokesperson for the Clinton campaign did not respond to the Washington Examiner's request for comment.