The boy band stars were watching the show at the Barclays Center in New York from the audience and, like many others, were shocked when the 20 year old ripped off her bodice to reveal rubber underwear and then proceed to grind up against Robin Thicke during a raunchy rendition of Blurred Lines.
But Styles was far from offended by Miley's act, insisting, "I thought it was vanilla. I would feel comfortable watching it with my grandma."
But bandmate Tomlinson wasn't so sure - because he wouldn't want his young sisters watching Cyrus' act: "I'm just glad I didn't bring my little sisters because, actually, I did plan to bring them."
Miley's performance has upset officials at America's Parents Television Council, who have attacked Mtv bosses for airing "unacceptable" performances from the former Hannah Montana Lady Gaga at the Video Music Awards on Sunday (25Aug13).
Ptc director of public policy Dan Isett adds, "Mtv marketed adults-only material to children while falsely manipulating the content rating to make parents think the content was safe for their children.
"Mtv continues to sexually exploit young women by promoting acts that incorporate 'twerking' in a nude-colored bikini. How is this image of former child star Miley Cyrus appropriate for 14 year olds?"