Simon Cowell splashed out on jewellery for his girlfriend's birthday

A source said: "It was a happy, relaxing day. Everything with them is great."

During the evening, Simon, 54, threw a small dinner party for Lauren at upscale Chinese restaurant Red Stixs in the Hamptons and their entire table sang 'Happy Birthday' as the brunette beauty was presented with a cake.

And it seems the eatery is a big hit with the couple, who have been enjoying a vacation in the New York resort.

A source told E! News: "They've been there a lot this summer. They seem to really love it."

And the pair are currently said to be planning another holiday with Eric.

An insider said: "It will be on a boat. Everyone's really looking forward to it."

The music mogul recently tweeted about how much he was enjoying spending time in the Hamptons.

He wrote: "Back to London in a week. Have loved the Hamptons. A very special place."

Simon also shared a number of pictures of his dogs Squiddly and Diddly playing in the sand.