Pamela Anderson and Tommy Lee
With ex-husband Tommy Lee by her side and a room decked out in her favorite color – pink – Pamela Anderson
turned the big 4-0 with an exclusive Planet Hollywood Hotel birthday bash in Las Vegas on Saturday.
The party didn't stop until 6 the next morning.
"She was having a ball," one reveler tells PEOPLE. "You would never guess she's 40."
Having recently returned stateside from her trip to Finland
, the blonde bombshell's birthday weekend began with a quiet afternoon Thursday basking in the sun by the Planet Hollywood pool with her parents and two children: Brandon, 10, and Dylan, 9. The boys later caught her stage show
, The Beauty of Magic
Saturday brought the real celebration. Following the show, Anderson, still wearing her one-piece-swimsuit stage costume, was greeted backstage with a cake that read, "Happy Birthday Pamela."
While Lee, 44, sat back smiling, Anderson's magic-show costar, Hans Klok, gifted her with an autographed copy of Harry Houdini's only book, written in 1920. "She made Tommy and David LaChapelle touch Houdini's autograph for luck and magic," according to an observer.
While Anderson and Lee remained coy backstage, they were more flirtatious at her private party in the hotel afterwards.
"They were definitely close to each other, cuddling and being quite affectionate," the partygoer told PEOPLE. "They clearly love each other and have tremendous passion for each other."
By the time the festivities wound down Sunday morning, Anderson headed to her room – clad in pink balloons and matching flowers.