The Lord of the Rings star was thrilled when he learned he'd be making out with the actress in the promo - but admits he went to great lengths to try and make sure he didn't upset her new husband Brian Austin Green.
Monaghan initially spoke to his co-star about what would be appropriate onset as they played passionate and fiery lovers and he felt the shoot went well.
But his best intentions were wrecked days later when the news of the video leaked and he was asked about the project.
He says, "I did all these interviews post the Eminem thing and they (reporters) said, 'How was it kissing Megan Fox?' And I said, 'It was Ok, it was good' - 'cos I wanted to be respectful of their marriage.
"And then it came out that I was, like, non-plus about the fact that I was making out with Megan Fox, which wasn't true; I had a great time, a very enjoyable time."
And then the gay rumours started.
He adds, "It didn't quash the gay rumours about (Lord of the Rings co-star) Elijah Wood and I."