Sen. Tim Kaine, D-Va., said Tuesday he wasn't particularly concerned when he learned that the father of the man who shot and killed 49 people at a gay nightclub in Orlando, Fla., sat directly behind Hillary Clinton during a campaign rally this week in the Sunshine State.

"I'm definitely not concerned about the security at the events because we just have wonderful people working for us who really are doing a good job in trying to make sure we are secure," the senator told reporters in Texas.

"And so this is – this is not a concern I have, but that's because of the professionalism of the team," he added.

Clinton appeared in Kissimmee, Fla., Monday evening 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!"

Unbeknownst to the Clinton campaign, however, was the fact that Seddique Mateen, the father of nightclub shooter, was seated directly behind the Democratic presidential candidate.

Mateen was spotted first by a local NBC News affiliate, WPTV.

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

Mateen's son, Omar, entered the Pulse nightclub on June 12 armed with handguns and an AR-15-style rifle, murdering 49 patrons and wounding 53 more.

The gunman was killed later in a shootout with law enforcement agents.

WPTV stopped Mateen immediately after the rally Monday and asked him about his presence at the campaign event.

"Hillary Clinton is good for United States versus Donald Trump, who has no solutions," he said.

Mateen added, "I was invited by the Democratic Party; I'm a member."

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

He was also asked if he thought anyone would be surprised to see him at the rally. He answered, saying, "Why should they be surprised? I love the United States, and I've been living here a long time."

The elder Mateen's background is a colorful one, and his endorsement of Clinton this week could prove a headache for the former secretary of state's campaign.

Along with voicing support for the Afghan Taliban, Seddique Mateen also stirred controversy by posting apparently anti-LGBT comments on social media.

"God will punish those involved in homosexuality … [it's] not an issue that humans should deal with," he said on Facebook after the Pulse shooting.

He eventually walked back these remarks, and said in an interview with CBS News that his now-deceased son did not, "have the right, nobody has the right to harm anything, anybody."

"What a person's lifestyle is, is up to him. It's a free country. Everybody has their own choice to live the way they want to live," he said.

Though the Clinton campaign maintained Tuesday they knew nothing of Mateen's attendance at the rally, the Washington Post pointed out he was likely on the Democrats' radar prior to the campaign event in Kissimmee.

"Mateen made a $250 donation to the Democratic Congressional Campaign Committee, which would have placed him on the radar of Democratic groups inviting voters to rallies," the Post reported.

A Clinton spokesman eventually said late Tuesday evening that the Democratic candidate rejected Mateen's endorsement.

"She disagrees with his views and disavows his support," said spokesman Nick Merrill.

Kaine has issued no such rebuke.

Reporters failed to press the Virginia senator Tuesday with questions about Mateen's support for the Afghan Taliban. Media also passed up the opportunity to question Kaine about Mateen's past comments on members of the LGBT community.