The famous pair - who announced their marriage separation in March 2014 - have managed to remain on friendly terms, and the Coldplay frontman treated her to the intimate birthday bash at her Los Angeles home.
According to the New York Post newspaper's Page Six column, the star invited some of Gwyneth's colleagues from her lifestyle newsletter, Goop, and some parents whose children attend the same school as their 10-year-old daughter, Apple, and their eight-year-old son, Moses.
Despite their separation, the former couple are still on good terms as an insider confirmed the pair had acted like ''best friends'' at the birthday bash.
They said: ''[Gwyneth and Chris] were very friendly to each other. It was like they're still best friends.''
One person who was not there to join in the fun was Chris' rumoured girlfriend, 'The Hunger Games' actress Jennifer Lawrence.
But their relationship is still said to be going strong as they enjoyed a romantic ride on a big wheel in Las Vegas on Friday (26.09.14).
A source said: ''The cabins usually accommodate up to 40 people, but Chris and Jennifer booked a private one for some alone time.''
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