Jennifer Aniston celebrates with Courteney Cox

Jennifer Aniston and Justin Theroux celebrated their engagement with a dinner with Courteney Cox on Monday (27.08.12).

While Justin proposed in New York earlier this month, the pair took the opportunity to enjoy a celebratory meal with Jennifer's former 'Friends' co-star and close pal in Los Angeles this week, when they dined out at the Sunset Tower Hotel's Tower Bar.

An onlooker told People magazine: ''Jennifer looked adorable! She looked so pulled together and very chic. She was dressed casually, but in heels.

''They were very calm and carrying on a regular dinner conversation. Jennifer had a big smile on her face. She and Justin both looked very happy.''

The restaurant holds special memories for the happy couple as it is the same place where they were first spotted together publicly, enjoying a romantic dinner together in May 2011.

Meanwhile, Jennifer, 43, is said to be ''overwhelmed'' by her eight carat diamond engagement ring.

A source recently said: ''It's a huge emerald-cut diamond. It's a rectangle with tapered diamond baguettes on the sides. It's beautiful.

''Just after Jen got engaged, she called all her friends and told them about it. She was so happy and said she loves the ring. I think she was overwhelmed and overjoyed by the size and beauty of it!''

Jennifer and Justin have been friends for years but only started dating after filming the movie 'Wanderlust' together.