The backdrop at Hillary Clinton’s Orlando-area rally couldn’t get much stranger.

In a startling appearance Monday evening, the father of ISIS-inspired Orlando nightclub gunman Omar Mateen showed up just steps away from the Democratic nominee, cheering her on and waving an American flag in the background – even as she paid tribute to the victims of his son’s terror rampage and condemned his “hatred.”

Seddique Mateen’s presence was first noticed by WPTV in Florida. The affiliate later interviewed Mateen, who held up a large, yellow pro-Clinton banner calling her “good for national security” and “gun control laws.”

Though Mateen claimed he had been “invited” to the Kissimmee, Fla., rally outside of Orlando, he also suggested the invitation may have come in the form of a mass email.

The Clinton campaign said Tuesday they were not aware of his presence.

"The rally was a 3,000-person, open-door event for the public,” a campaign official told Fox News. “This individual wasn't invited as a guest and the campaign was unaware of his attendance until after the event."

Still, Mateen’s presence right behind the candidate in full view of the cameras seemed to clash with her message, as she thanked local leaders and officers who responded to the June shooting at Pulse Nightclub, which left 49 people dead. It was the worst terror attack on American soil since 9/11.

“I know how many people, family members, loved ones, friends are still grieving,” Clinton said Monday. “We will be with you as you rebuild your lives … because we can’t ever let that kind of hatred and violence break the spirit, break the soul of any place in America.”

As she spoke, Mateen’s father could be seen behind her, at one point appearing to snap a photo with his phone before donning a red cap. 

Adding to the bizarre appearance is the father’s own background, as someone who has voiced support for the Taliban and at one point declared himself the leader of a “transitional” Afghanistan government. According to reports, he hosts a TV talk show that airs in California and is aimed at Afghans living in the U.S. 

After the shooting, Mateen also vehemently condemned homosexuality – but then suggested his son had no right to open fire inside the gay nightclub.

When WPTV first tried to interview him on Monday after his rally appearance, he said only that he’d been “cooperating” with the FBI.

But, according to the network, he wanted to give an interview when the reporter ran into him at a rest stop later that night. In the interview, Mateen claimed he had been “invited” by the Democratic Party.

But when asked if he was personally invited or received a chain email invite, he said, “I’m a member, so as a member I get the invitation, so it’s nothing particular about it.”

He said, “It’s a Democratic Party so everybody can join.”

He called Clinton “good for [the] United States versus Donald Trump.” As for his son’s actions, he said he wishes his son had joined the Army and fought ISIS.

“That would be much better," he told WPTV.

Fox News’ Tamara Gitt contributed to this report.