Jennifer Aniston and Justin Theroux's relationship is getting serious after the pair spent the entire weekend together.

The former 'Friends' star - who was previously married to Brad Pitt and has dated Vince Vaughn and John Mayer - has reportedly been getting to know the 'Your Highness' actor "for a while" and although they are not ready to announced their relationship to the world, they are both determined to make it work.

A source told X17 Online: "These two are jumping into this head-first. They're together all the time. But they sneak around and do everything they can not to be photographed together. Jen doesn't like her relationships to go public before she's ready."

While Justin visited Jennifer at her home on Friday (20.05.11), the couple had a romantic lunch at the Beverly Hills hotel on Saturday (21.05.11) before leaving together.

Jennifer then threw a small party at her house on Sunday (22.05.11) with the actor and a few other close friends in attendance.

Last week after the new couple were spotted on a dinner date, a source said: "Jen and Justin have recently started dating. They've known each other for a while, but they're more than friends now. They're cautious - they're both taking it slowly."