Paris Hilton helped celebrate Nicole Richie's birthday yesterday, and we just couldn't help but start singing "SanaSa!"

The blonde socialite shared several throwback posts in honor of her former bestie's 36th birthday yesterday, shouting out to her about all the good times they've shared.

"Happy Birthday @NicoleRichie," she wrote. "Looking thru all these photos brings back so many special & amazing memories! Just wanted to let you know that I am so happy for & proud of you. Such a beautiful family you have created & loving your new TV show @NBCGreatNews, so hilarious!"

A post shared by Paris Hilton (@parishilton) on

She continued, "I will always think of you as a sister & think of you often. Love & miss you #SanaSa #BillAndSill."

Of course, many of these memories include their five seasons on The Simple Life together.

From their catchphrase "That's Hot" to singing "SanaSa" all over the country, these two never failed at making us laugh. So in honor of Paris' hilarious throwback posts, we compiled a few more of our favorite memories from the show.

Watch the video above for some serious nostalgia!

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