LOHAN’S EX CITED FOR BATTERY AT CAESARS

Wild-child heiress Courtenay Semel is in trouble after whacking a Caesars Palace security guard during an argument after losing her cell phone, sources said.

Semel, whose father Terry Semel is a former CEO and chairman of Yahoo!, was earlier partying with Kourtney Kardashian, who had co-hosted a BestofVegas.com launch party with Nicky Hilton.

The incident occurred after 3 a.m., after Semel left Pure Nightclub at Caesars Palace with friends. She returned after the club was closed and complained to a security guard that she lost her cell phone.

Semel, who has been romantically linked to Lindsay Lohan and TV reality star Tila Tequila, was cited for battery after slapping the guard on the back of the head, according to a source.

Semel, 28, appeared in E!’s reality TV series “Filthy Rich: Cattle Drive” in 2006 with Kardashian and a roster of super-rich kids.

She was detained by Caesars Palace security and given an early October court date.

Semel and Lohan dated late last year before the “Mean Girls” star developed a relationship with DJ Samantha Ronson.

–NORM CLARKE, Vegas Confidential