Jennifer Aniston says falling in love with Justin Theroux is the best thing to happen to her since she reached her 40s.

The 46-year-old actress has been in a relationship with the 43-year-old star since 2011 and she admits finding happiness with her fiancé has been the most wonderful experience.

When asked what the best thing to happen to her in her 40s has been, she told PEOPLE: ''Justin. He's the best thing this decade.''

And Jennifer - who was previously married to Brad Pitt - can vividly remember the first time she ever met the 'Wanderlust' hunk.

The 'Cake' star first met Justin on the set of comedy movie 'Tropic Thunder' - which he briefly appeared in and co-wrote - in Hawaii in 2008 and although she immediately knew she was attracted to him, she wasn't convinced about his fashion sense.

She recalled: ''He was wearing black, black, black and I started to sweat just looking at him.''

Although she is occasionally unconvinced by his choice of clothes, Jennifer insists Justin picked out the most perfect engagement ring for when he popped the question.

She said:''I just think it's so beautiful. I love it because he picked it, put it into a setting and it's simple.''