Britney Spears and Jason Trawick

Great news guys -- Britney Spears' fiance proved ... once and for all ... size really doesn't matter! Sadly, this only applies to diamond rings.

Voila -- the first photos of Britney Spears' new engagement ring ... snapped last night as the singer and fiancé Jason Trawick partied the night away in Las Vegas.

3-carat round stone ... diamond-paved band ... not too shabby for the world's favorite 30-year-old pop legend.

TMZ broke the story -- Britney's hosted the intimate engagement celebration at the Planet Hollywood Resort and Casino, before taking the ring public at Jason Trawick's big celebratory dinner at the Chocolate Lounge in the Sugar Factory Resturant.

After the big dinner ... they hit up the Chateau nightclub and danced until the world ends.

Britney Spears will finally show off her engagement ring TONIGHT -- but before it goes public, she's holding a private gathering in Vegas to give her friends and family the first peek ... TMZ has learned.

Sources close to the couple tell TMZ ... the intimate event will take place at the Planet Hollywood Resort and Casino BEFORE Jason Trawick's big celebratory dinner.

We're told the owner of the PH -- Robert Earl -- will personally attend the event ... and plans to make a toast to the happy couple.

Jason Trawick jumped the engagement gun ... 'cause Britney Spears just posted a message hinting that he ALREADY popped the question ... and TMZ has learned she said yes!

Britney just went to her Facebook page and wrote, "OMG. Last night Jason surprised me with the one gift I've been waiting for. Can't wait to show you! SO SO SO excited!!!! Xxo."

Sources close to the couple tell TMZ ... Jason proposed last night ... and to celebrate, he organized a giant party in Vegas.

TMZ broke the story ... Britney knew Trawick was going to pop the question ... but it was SUPPOSED to happen tonight. Seems he just couldn't wait!

Sources close to the couple tell us ... the MASSIVE celebratory dinner will go down tonight at the Chocolate Lounge at the Sugar Factory in the Paris Hotel ... because Brit Brit LOVES chocolate.

We're told there will be a chocolate fondue fountain and all the men will get chocolate truffle cigars.

After dinner ... the gang is set to go to Chateau nightclub and party the night away.

We're told everyone involved in the fiesta has received specific marching orders -- anything Britney wants, Britney gets.

Britney Spears is getting engaged to boyfriend Jason Trawick, TMZ has learned.

Multiple sources who are definitely in the know say Jason plans to pop the question tonight ... in Las Vegas.

We're told Britney knows they're getting engaged, so it's not going to be a big surprise.

Sources say Britney's conservators have given their stamp of approval. The matter will go before the judge in the conservatorship case but it's virtually certain Brit will get the judge's sign off.

And we're told ... Jason did it the old fashioned way ... by asking Britney's dad, Jamie Spears, for permission to marry his daughter.

And they're also doing it the new-fashioned way ... we've learned there WILL be a prenup.

Brit Brit was seen with the ring poking out of her sleeve (see above) when she left a spa in the Valley on Wednesday. The rumor was ... she and Jason Trawick were set to get hitched and she was going to announce it on Twitter yesterday. Instead, she just announced a tour giveaway.

As you can see from the pics above, Brit has been wearing the ring for the past six weeks, and it looks more like a flower of some kind than a giant diamond.

Sources close to the couple tell TMZ ... they are still doing great together, but Jason has decided to step aside as her agent.

Trawick has left William Morris Endeavor to create an arts and entertainment division for a company called Famos LLC, whose partners include musicians Dave Stewart and Mick Jagger. The company will specialize in promoting artists who have a digital reach.

Store employees tell us Brit Brit usually comes by every year around the holidays to buy Xmas toys and other seasonal goodies -- no word on what she bought this time.

As we previously reported, Britney claims the person on the tape is not her -- and her lawyer has already threatened legal action against everyone involved in its release.

Britney just took to her twitter to make the announcement -- one day after a phone call was released which allegedly featured Britney admitting that Jason had beat her up.