Britney Spears, Jason Trawick
Britney Spears and boyfriend Jason Trawick are supposed to get engaged... tonight!

Britney Spears is set to walk down the aisle for the third time with her boyfriend Jason Trawick.

According to reports, Jason plans to pop the questions tonight as part of his 40th birthday celebrations in Las Vegas after going ring shopping on Monday.

The couple who have been dating since 2009 apparently discussed the engagement beforehand and Britney is said to be very excited. reported that a source close to the star and her talent agent beau said that Trawick has already brought a "diamond bauble" for the star.

The source told the celebrity news website: "Don't expect anything too massive or obnoxious. This ring will be classy and under 4-carats."

Meanwhile, TMZ has also learned that the happy couple plan to sign a prenup before getting married.

The old fashioned agent, even went to Britney's' father, Jamie Spears, to ask for her hand in marriage, and was over the moon when he received the go ahead.

Here's hoping its third time lucky for the embattled singer who famously got hitched to long time friend Jason Allen Alexander in Las Vegas In 2004.

She then exchanged vows with backup dancer Kevin Federline later that year. The couple, who have two sons together called time on their marriage two years later.