Jennifer Aniston reportedly waited six weeks to share her engagement news.

It was widely reported that Justin Theroux asked the Hollywood beauty to marry him on his 41st birthday earlier this month. However, British magazine Heat has revealed the pair actually got engaged during their holiday to Italy in July.

"They kept his proposal to themselves because they wanted to wait until he had the ring, and also they wanted to make a formal announcement when they were ready," a friend of the couple told the publication. "Justin also wanted to tell his ex-girlfriend [Heidi Bivens] in person, so she didn't find out from the press."

The insider added that the formal engagement on August 10 was pre-planned at an intimate location.

"On Justin's birthday they went to Blue Hill, their favourite restaurant in the Village - it's dark and quiet and they're always left alone there. Over champagne, they decided they would announce the engagement that weekend. Jen is happier than I've ever seen her," the friend revealed.

Insiders say that Jennifer knew about the engagement long before the informal proposal. Sources insist the pair - who have been dating for around 15 months - have spoken about marriage before.

"They both knew where they were headed with this relationship and had talked about marriage at Christmas. But they knew it wasn't the right time to get engaged and let the information leak out. For Jen, getting married again is a huge deal," the friend added.