After a recent trip to Cabo San Lucas, Mexico, for her 41st birthday, Jen couldn't wipe the smile off her face, and now it seems we might know the reason why.

A source told Heat Magazine: "How could she anything but on top of the world? She says the sex is amazing. They have great chemistry across the board – sexually and intellectually."

The former Friends star has made no effort to hide her feelings for the Scottish heartthrob either, previously saying that he's 'absolutely the most lovely and sort of self-deprecating person'.

The couple's steamy romance is still reportedly casual but Heat's source continued to say that Jen is just enjoying the moment and not getting stressed about where the relationship is heading.

And by the looks of it, whatever Mr Butler is doing for her, it seems to be working because Jen looks happier than ever.

/Metro.co.uk/