Pamela Anderson has celebrated her 40th birthday with ex-husband Tommy Lee.The former 'Baywatch' actress and Tommy partied at the Planet Hollywood Hotel on Saturday night, until 6am the next morning.One party goer said: "She was having a ball. You would never guess she's 40."The birthday celebrations began on Thursday when Pamela arrived at the Planet Hollywood hotel with her parents and two sons 10-year-old Brandon and nine-year-old Dylan.The boys later watched their mother perform as a magician's assistant alongside Hans Klok in his stage show 'The Beauty of Magic'. After Saturday's show the actress was presented with a cake saying "Happy birthday Pamela". Klok gave her an autographed copy of Harry Houdini's only book, written in1920. A source said: "She made Tommy and photographer David LaChapelle touch Houdini's autograph for luck and magic."At the private party Pamela and Tommy, 44, appeared to be reigniting their passion for each other. A source said: "They were definitely close to each other, cuddling and being quite affectionate."They clearly love each other and have tremendous passion for each other."On Sunday morning Pamela retired to a bedroom filled with pink balloons and matching flowers.