'Charmed' actress was not in a relationship with Jennifer Aniston's partner.
The 39-year-old actress said via twitter: ''Completely false. We were co-workers & great friends but never dated.''
The pair met on the set of 1997 thriller Below Utopia where their roles as an on-screen couple were rumoured to have led to a real-life romance.
However Alyssa has clarified that he was in fact involved with her friend, Kathryne Dora Brown, while they played lovers on camera.
She clarified: ''He dated my best friend at the time. I love that guy.''
Alyssa and her husband David Bugliari welcomed baby Milo on August 31, 2011.
Meanwhile Justin, 40, and Jennifer, 43, share a home together in Los Angeles.
Jennifer Aniston is also looking for a home in London while she shoots low-budget comedy drama 'Miss You Already' in the UK capital and has instructed her representatives to find her a property to rent.