Drink up! Dakota Fanning kept her 21st birthday celebrations going on Watch What Happens Live on Tuesday, Feb. 24. As she sipped on cocktails with host Andy Cohen and fellow guest Lisa Rinna, the Effie Gray actress dished about the Olsen sisters, her Runaways costar Kristen Stewart, and more.

A caller started off the fun by asking the former child star if she’d rather have Mary-Kate or Ashley Olsen as her best friend. "Here's the thing," Fanning said. "Their younger sister Lizzie [Elizabeth Olsen] is who I know the best. We went to the same high school, we have a lot of mutual friends, and we did a film together [Very Good Girls.]"

"I've only truly met them a couple of times," she continued. "I don't think I know them well enough to answer that question." As for who has the best fashion sense? "Both!" she said. "Both of them are totally lovely."

Fanning also played Plead the Fifth and Never Have I Ever Whatsoever on the Bravo show. Like the Olsen question, she had nothing but nice things to say about her 2005 War of the Worlds costar Tom Cruise. She insisted that the actor never did anything odd on set.

"You're like lifer friends with him," Cohen said. Fanning replied: "I really am."

Other tidbits: Fanning was pressured to admit one of Stewart’s most annoying traits, and whether or not she's ever watched porn. Plus, did the birthday girl ever lie to get an acting gig?

Find out her answers in the video above!