Rihanna and Ashton Kutcher hooking up?

Rihanna and Ashton Kutcher ... could it be?

In what may or may not have been the walk of shame, the pop superstar was spotted leaving Kutcher's Los Angeles mansion in the wee hours on Thursday, after arriving four hours before.

What makes it seem like a hook-up, as opposed to a friendly visit? The fact that earlier Wednesday, the "S&M" singer went out for the night, dining with a pal at swanky Santa Monica restaurant Giorgio Baldi's, according to RadarOnline.com.

If there's anything to this late-night rendezvous, we're betting tabloid offices will literally combust, as both stars' love lives are a constant subject of intense interest - namely RiRi's ongoing saga with her abusive ex Chris Brown and the "Two and a Half Men" star's sudden split from wife Demi Moore last November.