Nicole Richie and Paris Hilton have a "sisterhood"

Nicole - who recently reunited with Paris to film a new show, 'Paris and Nicole: The Encore' - told PEOPLE: "I think anytime you are separated from your loved ones, it's not the best moments.

"But Paris and I have more of a sisterhood than I would say, a standard friendship. We've been in each other's lives for as long as I can remember since we were two. So this is just, it's life and it's just been so exciting to be able to shoot this show again. It was great."

Paris, 43, feels similarly strongly about their friendship.

The blonde beauty - who is married to Carter Reum - explained: "I just feel so lucky just to have a lifelong friendship like we have - a friendship that's longer than most marriages."

Paris feels "proud" that their friendship has survived so many ups and downs over so many years.

She said: "We've just been through everything together in life since we were little babies.

"I'm just so proud of how much we've grown and just all the experiences that we've been through in life. It made us these really incredibly strong, resilient and amazing women, and I'm really proud of us."

Paris and Nicole starred alongside each other in 'The Simple Life', the hit reality TV show, between 2003 and 2007.

And Paris feels proud of the show's legacy.

She said: "People love the show. It's so timeless.

"It's brought so much happiness to so many different generations and really stood the test of time and has become the blueprint for so many others."