Officers from Ventura County Sheriff's Department responded to an incident of trespassing at the address and later arrested 40 year-old Alexander.
Alexander, 40, has been charged with two counts of misdemeanour battery, one count of misdemeanour vandalism and one count of misdemeanour trespassing, following an incident at the singer's Los Angeles home.
Sergeant Cyrus Zadeh said Alexander had been able to find his way onto the property and was confronted by security.
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It is understood that the intimate wedding ceremony between the singer, 40, and her 28-year-old fitness trainer partner was to be held on Thursday.
Shortly before the incident, her former partner Alexander posted an Instagram live story from near to the property, in which he said he was there to "crash" the wedding.
Spears and Asghari became engaged in September last year, with the singer joking that the proposal was "way overdue".
A 13-year conservatorship which had controlled her life was terminated by Los Angeles Superior Court in November last year.
A source quoted by American publication People had said the ceremony on Thursday was to be attended by around "60 guests of those in their close circle".
Spears has two children, Sean and Jayden, with ex-husband Kevin Federline.
It will be the singer's third trip to the altar, having divorced Federline in 2007 and Alexander in 2004 after their marriage earlier that year.
In May, the singer announced the loss of her "miracle baby early in the pregnancy".
She had revealed she was pregnant a month earlier, saying she had taken a test after Asghari teased her about being "food pregnant".
According to TMZ, Spears' brother Bryan will attend the ceremony but her sister Jamie-Lynn and parents will not be present.
Spears has been estranged from members of her family after she was placed under the controversial conservatorship in 2008, which controlled many aspects of her life including her finances, amid substance abuse and mental health issues.