Rob Lowe Says He 'Briefly Had a Thing' With Demi Moore In The '80s

Rob Lowe is looking back on a short romance he had with Demi Moore ...

revealing they briefly hooked up early on in their Hollywood careers. Rob told Kelly Ripa he "briefly had a thing" with Demi in the '80s during their time in the Brat Pack ..

. admitting to the hookup on Kelly's podcast, "Let's Talk Off Camera." The way Rob tells it .

.. he and Demi banged at some point in the mid-'80s, before she got engaged to Emilio Estevez , another member of the Brat Pack.

Rob joked the hookup was part of a "big, big sex orgy" among the cast of the 1985 movie "St. Elmo's Fire." But that wasn't the only movie in which Rob and Demi were paired up on set .

.. they also starred alongside one another in another flick, 1986's "About Last Night.

" Looking back, Rob explains ...

"Anytime you put young 20-something men and women together, hookups are inevitable." Rob and Demi remained friends after their brief fling ..

. and he even went to her wedding to Bruce Willis ..