And so, in honour of Drew's 46th birthday this week, Cameron, 48, made a surprise Zoom appearance on the Drew Barrymore Show. During their chat, the two ladies talked about their decades-long bond - and it was certainly revealing!
WATCH: Take a peek inside Cameron Diaz's kitchen!
Amongst other revelations was the very unusual nickname the pair have for each other – 'Poo Poo'.
"It started out as classic boy humor and it just evolved into a true term of endearment. And then it just stuck...we love it...it will never change," Drew explained.
"When we're at a restaurant she'll say to the waiter, 'Ask Poo Poo what she wants.' And people will be like, 'What?' We call each other Poo Poo. I call her Poo Poo. She's in my phone as Poo Poo," Cameron added.
Drew and Cameron are the best of friends
In fact, the pair are so close that Drew further admitted that Cameron is the only friend she would let share her bed. She said: "I don't like co-sleeping with anyone, it's a thing. I don't know why but it's my thing.
"If it's like a lover then obviously that’s different, but no friends. I will sleep in a bathtub, I've slept on a pool table, like you name it, but this one...Oh my gosh.
"We've lived together for periods of time, been roommates. I've slept in a tent while my fever was breaking on a Chilean mountain in a thunderstorm in, like, Patagonia. I mean, yeah, we've been everywhere together."
Cameron made a surprise appearance to celebrate Drew's birthday
Traditionally, the best friends will spend their birthdays together, with Cameron explaining: "We are not big gift givers, we're more about experience, so we always try to go someplace and do something with the girls and be together. Cook, eat, hang and stay up all night and just have the best time."
She sweetly added: "Truly, one of the great joys of my life, is our friendship. When I think about you, literally, I will cry, because I just think you're so special and to celebrate you is the absolute — every year, it's one of my favorite times of the year is to get to celebrate you."
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