Zac Efron admits the fight he was involved in in March was the ''most terrifying'' time of his life.

The 26-year-old actor - who endured two stints in rehab last year - was recently involved in a mysterious altercation with a ''homeless guy'' in Los Angeles and admits he had never been more scared than when the man pulled out a knife.

Recalling the incident, he told The Hollywood Reporter: ''I had a friend come pick me up late at night -- we were looking for a place downtown to get a bite and catch up.

''We were having trouble finding somewhere - a lot of places were closed - and the car ran out of gas off the 110. It was ridiculous. We had to pull over, and I called Uber.

''[While waiting] a homeless guy, or vagrant, tapped on the driver's-side window. Before I knew it, he [my friend] was out of the car, and they started fighting.''

Zac claims he got out of the car to help his friend - who was previously reported as being a bodyguard - ''disarm'' his opponent, and he was relieved when police arrived to diffuse the situation.

He added: ''I saw that [the homeless man] was carrying some sort of a knife, or shank, and I got out of the car to disarm him.

''At some point, he dropped the knife, and I got hit pretty hard in the face - and almost instantly the police were there to break up the fight...

''It was the most terrifying moment of my life.''

Following the terrifying incident, friends of the 'Neighbors' actor - who broke his jaw in a fall at home last November - admitted they were worried about his sobriety and questioned the intentions of his pal, who they claimed was actually a drug dealer.