Kate Middleton wears Princess Diana's tiara at palace party

Kate Middleton attended the Queen Mary’s Lover’s Knot tiara (not pictured) on Tuesday for a palace party. (Reuters)

Kate Middleton paid tribute to the late Princess Diana on Tuesday by donning one of Prince William’s mother’s favorite tiaras.

Middleton attended Queen Elizabeth II’s Diplomatic Reception at London’s Buckingham palace Tuesday evening with William. She wore the Queen Mary’s Lover’s Knot tiara, which was one of the late princess’ favorite jewelry items, with her hair placed in an up-do.

This is the third year Middleton, who is pregnant with her third child, wore the tiara, according to the Court Jeweller. Middleton wore it in 2015, the first time anyone had worn the jewel since Diana passed away in 1997.

The tiara, also referred to as the Cambridge Lover’s Knot tiara, is one of the oldest royal jewels and was first commissioned by Queen Mary, the Court Jeweller reported. She sacrificed a tiara from her own jewelry collection to make it. Mary passed the tiara to Queen Elizabeth II when she died in 1953.

Queen Elizabeth wore the jewel a few times before she gifted it to Diana in 1981 — when the princess married Prince Charles.

Princess Diana was photographed wearing the Queen Mary’s Lover’s Knot tiara, also often referred to as the Cambridge Lover's Knot tiara. (Reuters)

The tiara was one of the two that Diana was photographed wearing on her head.