While the headlines have been full of news of Prince Harry's royal engagement to Meghan Markle and speculation about what they might wear for the momentous occasion, his pregnant sister-in-law Kate Middleton has been making style waves of her own ... while wearing bridal white.

Middleton was spotted in a sparkling diamond tiara and soft white outfit while arriving to a winter party at the palace on Tuesday alongside Prince William. While her full look wasn't fully revealed, we did get a hint of her dress and some very familiar jewelry.

Kate Middleton 
Credit: Andrew Parsons / i-Images / Polaris

The royal wore Princess Diana's favorite tiara for the occasion, and she couldn't have looked more regal. She paired the statement piece with teardrop pearl earrings, a diamond necklace, and her embroidered outfit.

Kate Middleton 
Credit: Mark Cuthbert/UK Press via Getty Images

The glittering diamond and pearl tiara wasn't just Diana's favorite though—it's also one of Kate's. Middleton wore the headpiece to last year's winter reception as well, and she wore it to a banquet while visiting the Spanish royal family back in July.

The tiara was originally a wedding gift to Diana and remained one of her favorite pieces of jewelry. Looking at how lovely and timeless it is, we can see why.

We wouldn't be surprised if we spotted the beautiful tiara on Princess Charlotte's head one day too.