The 47-year-old actress was so infatuated with the music legend she used to wait for him to leave his Los Angeles home and take his post, and it wasn't until years later the 'Maggie May' hitmaker found out when the blonde beauty's ex-husband, Sean Penn, confessed her secret to him at a party.
She said: ''I was completely in love with Rod Stewart. I had a huge poster of him on my bedroom wall and thought I was going to marry him. I met him for the first time with Sean ... we were at a party and I was so nervous I was sweating.
''Sean introduced us both by saying, 'Robin was in love with you and used to steal your mail.' I did too, I used to take it from the mailbox outside Rod's house in Los Angeles.
''I was 15 at the time and had an older friend who drove. I would wait down the end of the drive just to see Rod walking out. It was so humiliating to see him as an adult and not be in love with him anymore. It breaks the magic.
''So I know what it is like to be a fan and those who never have been have no idea. It was insane. We would save up money to buy front row tickets to his shows for $250.''
While Robin was besotted with 68-year-old Rod during her teenage years, the 'Forrest Gump' star went on to marry Sean - who she started dating shortly after he split from Madonna - and admits the couple ''loved each other crazy'' and were ''never bored'' during their 14-year marriage.
Robin - who has daughter Dylan, 22, and 19-year-old son Hopper with Sean, who she divorced in 2010 - added in an interview with The Sun newspaper: ''With Sean we had this glue which kept us together. We drove each other crazy and loved each other crazy, we were never bored.
''It was my destiny to have children with Sean and that is beautiful.''