Credit: Splash News Online

Since getting engaged in December, Jessica Biel has kept her engagement ring from Justin Timberlake under lock and key with only recently debuting the humongous diamond on her ring finger!

No word on why the 30-year-old actress took so long to step out with her new bling, due to the sheer fact that it's clearly a bauble to brag about!

"The scrolling rope-style sides provide a vintage element, but the blackened platinum gives this style a modern twist," jewelry expert Michael O'Connor tells Us Weekly, adding that the center diamond (either radiant- or princess-cut) weighs in at at an impressive six carats.

O'Connor estimates the price tag for the jewel is approximately $130,000!

A source recently told Us that the couple, who dated on-and-off for nearly five years, plan to tie the knot this year. "The big day's this summer at a private estate," the source said. "Monique Lhuillier is [Jessica's] No. 1 choice for the dress."