Sen. Kamala Harris (D-Calif.) honored fellow 2020 Democratic presidential hopeful Joe Biden's son Thursday on the fourth anniversary of his death.

"Thinking of @JoeBiden, @DrBiden and the entire Biden family today," Harris wrote on Twitter.

"Beau Biden was my friend. We were AGs together, and you couldn't find a person who cared more deeply for his family, the nation he served, and the state of Delaware. Four years after his passing, I still miss him."

Beau Biden died on May 30, 2015, of brain cancer.

The 46-year-old served as attorney general of Delaware from 2007 to 2015 when he stepped down at the end of his term in office.

The former Vice President thanked Harris in a Thursday tweet.

"Thank you @KamalaHarris from me, Jill, & all the Bidens for your kind remembrance of Beau today," he wrote. "My dad used to say that you know you are a success as a parent when you turn & look at your child & realize they turned out better than you - I'm so proud of the man Beau became."

Beau was the second of Joe Biden's children to pass away - a car accident in 1972 killed his first wife, Neilia, and his year-old daughter Naomi.