Seddique Mateen, father of the Orlando nightclub shooter Omar Mateen was seen sitting behind Hillary Clinton at her rally, as she campaigned in Kissimmee, Florida.
The unexpected visitor caught the attention of some as he sat cheering for the Democratic Presidential candidate directly behind her on the seats chosen by the campaign staff.
Mateen is known for his controversial views on Afghan politics and homosexuality. He became more prominent after his son killed 49 and injured 53 at Pulse, a gay nightclub in Orlando, Florida.
His presence at the rally raised speculation about his closeness to Clinton.
"Hillary Clinton is good for United States versus Donald Trump, who has no solutions," he said, Charisma News reported.
"I support everything Clinton has to say, especially her gun control measures," adding that he had hoped his son could join the fight against ISIS.
In a move to express solidarity, Clinton began her rally speech by paying tribute to those who lost their life in the June 12 shooting incident.
After the campaign made headlines for Mateen, Clinton's campaign released a statement saying they were unaware of his attendance until after the event.
"The rally was a 3,000-person, open-door event for the public. This individual wasn't invited as a guest, and the campaign was unaware of his attendance until after the event."
Security is usually limited to metal detectors for public campaign rallies and only those sitting close to the candidate undergo additional checks.
"A presidential campaign should take a more cautious approach to selecting who's in the shot, but accidents happen," said a Republican staffer to ABC News.
Mateen has recently said that he was indeed "invited" to the rally.