Christie Brinkley spends July 4th with ex husband Billy Joel

Christie Brinkley and Peter Cook took a holiday from their bruising divorce war Friday - she barbecued with ex-hubby Billy Joel and he cavorted on the beach with his bikini-clad girlfriend.

Dressed in red, white and blue, Brinkley celebrated the Fourth of July by heading to the Piano Man's waterfront Sag Harbor house with their daughter, Alexa Ray.

Joined by family friends, the former couple hit a neighbor's house for some backyard barbecue and then returned to Joel's veranda with plates of food.

They could be seen laughing and joking around and even shared a tender hug at one point.

Joel, who is remarried, has been supportive of Brinkley in her scandalous split from Cook; Alexa Ray testified on her mom's behalf earlier this week.

Cook took a beating in the first two days of the trial, with revelations about his affair with a teenager and Internet porn habit.

When he showed up at Brinkley's home Friday morning to pick up 13-year-old son Jack, he wasn't relishing the thought of seeing the supermodel.

"Here we go," he said with a mix of resignation and exasperation. "[Let's] see how friendly she is."

Ten minutes later, he left with Jack - the son of Brinkley and ex-husband Ricky Taubman, but whom Cook adopted.

"I didn't see Christie when I went to the house," he said. "I just picked up my son."

Cook, 49, and Brinkley, 54, are battling over custody of Jack and Sailor Lee, 10, Cook's biological daughter.

Brinkley has custody and Cook has visitation rights, and he was scheduled to spend the holiday with Jack before the boy heads to summer camp Sunday.

Cook told the Daily News he was planning to spend the day at home, but he soon headed for the Sag Harbor Marina, where he and Jack took off in his fishing boat - the Sweet Freedom.

They joined another boat carrying gal pal Suzanne Shaw and a half-dozen other pals, and both vessels headed to a private beach in North Haven, across from Shelter Island.

Cook seemed to be having a ball with Shaw, who stripped down to a bikini and got on a Jet Ski with Jack.

She's scheduled to be a witness next week when the divorce case resumes - with a different kind of fireworks than you see on the Fourth of July. via