Jennifer Lopez and Marc Anthony Jennifer Lopez and Marc Anthony

Jennifer Lopez and her husband of four years, Marc Anthony, capped a night of club-hopping and show-catching by renewing their wedding vows. The ceremony took place at 3:15 am Sunday morning at Caesars Palace in Las Vegas, in the newly renovated Forum Tower Penthouse.

"It was totally a spur-of-the-moment thing," one source tells People. "They decided around 12:30 in the morning that they wanted to do it."

The exchange of vows was officiated by Reverend Steven Smith, with two friends serving as witnesses. By some accounts, the couple was in Sin City to belatedly mark Anthony's September birthday.

Lopez and Anthony became parents in February when they welcomed the arrival of twins Max and Emme.