Although tabloids have been consistently declaring for years that Jennifer Aniston is engaged, it's finally true. On Friday, boyfriend Justin Theroux popped the question to Aniston, his beau of over a year.

"Justin Theroux had an amazing birthday on Friday, receiving an extraordinary gift when his girlfriend, Jennifer Aniston, accepted his proposal of marriage," his rep revealed to People.

While the engagement is exciting news, fans of Aniston are dying to see the ring...something she has kept well out of sight for now. The actress was spotted back on the set of her new film, "We're the Millers" on Monday, but while paparazzi caught her, they failed to catch the sparkly ring.

According to E! News, even if paparazzi managed to get the golden shot of Aniston, she wouldn't have been wearing the ring because she was in character. While the world will have to wait a little to finally feast their eyes on Jennifer Aniston's new set of bling, we can definitely speculate what the star will have on her finger.

As Richard Wubnig, gemologist and jewelry manager for New York's Michael C. Fina explained, there are five popular engagement ring styles sweeping 2012.

1. Yellow Gold and Rose Gold

A blast from the past, yellow gold is making a major comeback. Originally big with leading Hollywood ladies in the 1930's, this ring would be a perfect for current leading lady Jennifer Aniston. According to Wubnig, yellow and rose gold add "extra visual interest," and is "elegant and timeless."

2. Emerald Cut Diamonds

Emerald cut diamonds practically scream glamour and red carpet. Wubnig describes the cut as "sophisticated yet edgy," and has seen emerald cut diamonds rise in popularity due to recent celebrity engagements. Although Kate Hudson and Beyonce can be seen rocking emerald cut engagement rings, we have a feeling Justin Theroux steered clear of this cut since it can also be seen on Angelina Jolie's engagement ring from Brad Pitt.

3. Colored Gemstones

While Jennifer Aniston and Justin Theroux are constantly spotted wearing matching black ensembles, Theroux could have gone with a ring that had a bit of a pop to it. A colored gemstone engagement ring adds individuality and style, explains Wubnig. These flashy rings have been popping up in the tabloids as well. Facebook's Mark Zuckerburg popped the question with a ruby engagement ring, and Kate Middleton is now the proud owner of Princess Diana's stunning sapphire ring. If Aniston is rocking a colored gemstone engagement ring, it's bound to stand out against her generally dark wardrobe.

4. Micro Pave and Halo

According to Richard Wubnig, micro pave rings definitely offer a "wow factor." If Theroux wanted to sweep Aniston off her feet, the micro pave engagement ring would have been the way. The ring gives off the illusion of a solid diamond surface, while actually being set with ultra-miniature diamonds. When the micro pave is in a halo setting (a ring or halo around the center gemstone), the diamond looks bigger and stands out more.

5. Vintage Glam

Vintage-inspired rings "combine romantic charm with the intricate metalwork of antique rings," explained Wubnig. For Hollywood royalty like Jennifer Aniston, a vintage glam inspired engagement ring would look absolutely stunning. One star that is already rocking a vintage glam style ring is Justin Timberlake's fiancée, Jessica Biel.

What kind of ring do you think Justin Theroux used to pop the question to Jennifer Aniston?

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