Jason Alexander, 40, livestreamed himself sprinting through woods in Thousand Oaks, California, as he approached the venue.
Before being confronted by security, he managed to get inside the rose-covered wedding area, where ‘Toxic’ singer Spears, 40, was due to marry her long-term personal trainer partner Sam Asghari, 28, on Thursday.
Alexander insisted Spears had invited him as she was his “first and only wife” before he admitted he was “crashing” the nuptials.
Alexander and Spears tied the knot in Las Vegas in 2004 but were married for just 55 hours before they had the marriage annulled.
A 10-minute long Instagram live video shows Alexander scaling a fence on the perimeter of Spears’ property, before he encounters a mob of security personnel and declares: “I’m Jason Alexander. The first husband. I’'m here to crash the wedding!”
He is also seen entering the wedding tent where planners were busy adding finishing flourishes to the venue.
Ahead of his run-in with security he could be heard yelling, "Don't put your hands on me," and demanding, "Where's Britney?" while ignoring security's pleas and orders.
Alexander also brands the event "b*******” while showing off floral arrangements, before his phone freezes.
During the on-off video, which occasionally cut out while it was running, Alexander was seen bounding up a fight of stairs to a second storey before getting into what appeared to be a bedroom, while yelling Spears’ name.
Alexander is also seen being caught by a member of security, who can be see holding a gun in his hand – which he keeps pointed towards the floor.
He also posted images and video to his Instagram declaring: “Follow the money” and “Freedom” dressed in a black baseball cap seen in the livestreamed clip – prompting one of his followers to comment: “Get help.”
The Ventura County Sheriff's Department raced to the scene after answering a trespassing call, with three police cars arrived at the singer’s Thousand Oaks home just after 2.30pm on Thursday, alongside a fire truck.
One witness told DailyMail.com: “It all happened very fast. Three cop cars just showed up and went screeching up her drive.
“We were all trying to figure out what’s going on, especially after the fire truck left.”
Captain Cameron Henderson of the Ventura County Sheriff’s Office said: “We are there investigating after reports that somebody was trespassing on the property.
“I don't know if he jumped over or how that happened but we are there investigating.
“I can't confirm who the suspect is, we have deputies on scene trying to figure everything out right now.”
Sgt Cyrus Zadeh of Ventura County Sheriff’s Office added to The Sun from the scene: “Earlier today we responded to the Britney Spears residence to a call that a trespassing was occurring.
“Four deputies plus a sergeant attended the incident.
“We contacted a male subject by the name of Jason Alexander on the property and he has been placed under arrest as of right now for an out of county warrant.
“We’re still conducting an investigation to determine if any other criminal violations occurred.”
Neither Britney nor Sam has addressed the incident.
Hours before the big day, details surfaced about the day.
Sources told TMZ the ‘Baby One More Time’ singer and Sam were planning to exchange vows in an "intimate" ceremony in front of a "very exclusive and small guest list of about 100 people" - with just one close family member.
The relative in question was Britney's older brother, Bryan, 45.
Her parents and sister Jamie Lynn, 31, with whom she has recently battled were excluded.
The drama comes after Spears finally found freedom after escaping her conservatorship that saw her finances controlled for 13 years.
Spears and Asghari got engaged in September 2021 after being together five years following their first meeting on the set of the singer’s music video for her track ‘Slumber Party’.
Spears announced in April she and Asghari were expecting a baby but a month later she suffered a miscarriage.
Twice-married mum-of-two Spears got hitched to dancer Kevin Federline, 44, the same year her marriage to Alexander was annulled, but it ended in divorce after they had children Sean Preston, 16, and Jayden James, 15.