Britney Gets New 5.5 Carat Diamond Ring

Britney Spears's hand is about to get a little heavier.

The pregnant pop star is getting an upgraded engagement ring – a gift from her husband Kevin Federline – to replace the one she picked out last year from jewelry designer Cynthia Wolff.

"I think it was because he wanted to buy her the diamond ring," a source close to Spears tells PEOPLE.

The new ring, also designed by Wolff, is quite a sparkler, says the source, who describes it as having a platinum band with a 5.5 carat round, single diamond set in a classic style.

Though Spears was spotted testing out a similar version of the ring over Memorial Day, friends say the real thing won't be delivered until later this month.

"Kevin is giving it to her, which is a huge gesture, I think," says the friend. "He's a real standup guy. It is lovely and she's very happy and excited. The gesture of the gift is huge."