We tend to imagine celebrities as impossible to impress.

They walk red carpets, meet movie stars for a living and spend their careers surrounded by some of the most famous people in the world.

But every once in a while, someone walks into the room who turns even a Hollywood star into a nervous fan.

And some of those moments have been absolutely unforgettable.

Helen Mirren Couldn’t Hide Her Feelings About Vin Diesel

Few people would have predicted this pairing.

Dame Helen Mirren once openly admitted that she had developed quite a crush on Fast & Furious star Vin Diesel.

After watching Diesel give a speech at an awards ceremony, Mirren was struck by how smart, funny and cool he seemed.

She publicly declared her affection for him — and also made no secret of wanting to appear in a Fast & Furious movie.

Eventually, she got her wish.

Mirren joined the franchise as Magdalene “Queenie” Shaw and later found herself filming scenes alongside Diesel.

Years afterward, she was still talking about their chemistry and how much she loved being around him.

Sometimes persistence pays off.

Mark Ruffalo Couldn’t Believe What Happened With Meryl Streep

Mark Ruffalo may be an Oscar-nominated Hollywood star, but put him beside Meryl Streep and suddenly he’s a fan again.

During an appearance on The Graham Norton Show, Ruffalo couldn’t hide his admiration for the legendary actress.

Then things got even better.

Streep gave him a kiss.

Ruffalo’s delighted reaction afterward said just about everything.

For a moment, the Hollywood leading man looked less like a movie star and more like someone who had just experienced the greatest day of his life.

Pink Turned Shy When Johnny Depp Appeared

Pink has performed in front of enormous crowds without appearing remotely intimidated.

Johnny Depp was apparently another matter.

Pink had previously admitted to having a crush on Depp.

Then Jimmy Kimmel decided to surprise her.

Depp suddenly walked onto the set.

Pink’s confident demeanor disappeared almost immediately.

She became visibly embarrassed and struggled to maintain her composure while Depp greeted her.

It was the kind of reaction millions of fans understood immediately.

Emilia Clarke Finally Met Joey From Friends

Before she became internationally famous as Daenerys Targaryen on Game of Thrones, Emilia Clarke was watching Friends like millions of other viewers.

And she had a particular fondness for Matt LeBlanc.

Years later, she found herself sitting beside him on The Graham Norton Show.

Clarke admitted she’d had a huge crush on him.

Then she made one request.

Could he ask her how she was doing in Joey Tribbiani’s unmistakable style?

LeBlanc obliged.

“How you doin’?”

Clarke’s reaction was priceless.

Suddenly one of television’s biggest stars looked like a teenager meeting her crush.

Winona Ryder and Keanu Reeves Had an Even Better Surprise

Sometimes the crush goes both ways.

Winona Ryder and Keanu Reeves have known each other for decades and famously starred together in movies including Bram Stoker’s Dracula.

But years later, while promoting Destination Wedding, something charming emerged.

They revealed that they’d had crushes on each other.

And apparently, the affection hadn’t entirely disappeared.

Their friendship became even more fascinating because Ryder has repeatedly joked that she and Reeves may technically have gotten married while filming Dracula.

Director Francis Ford Coppola used a real Romanian priest for their wedding scene.

Whether or not that makes them genuinely married, Reeves has happily played along with the story.

Sophie Turner Ran Away After Meeting Justin Bieber

Sophie Turner’s reaction may be one of the funniest.

Long before Game of Thrones, Turner was a major Justin Bieber fan.

Then she actually met him.

Turner later recalled being introduced to Bieber while visiting a house in Miami.

She managed to introduce herself.

Then she escaped into a closet and cried.

When she returned, things didn’t exactly get smoother.

Overwhelmed by the situation, Turner made an awkward peace sign and stuck out her tongue.

Even years later, she could laugh at how completely her brain seemed to stop cooperating.

Ariana Grande Got Emotional Meeting Jim Carrey

Ariana Grande’s longtime celebrity crush wasn’t a pop star.

It was Jim Carrey.

Grande had admired the comedian since childhood.

When she finally got the opportunity to meet him, maintaining her superstar composure proved difficult.

She became emotional and teared up.

It was a reminder that fame doesn’t erase childhood heroes.

You can sell millions of records and perform for enormous crowds — and still become overwhelmed when the person whose movies you grew up watching suddenly stands in front of you.

Fame Doesn’t Stop You From Being a Fan

That’s what makes these encounters so entertaining.

For a few seconds, the hierarchy of Hollywood disappears.

Oscar winners become nervous.

Pop stars blush.

Television icons forget what they’re supposed to say.

And celebrities who are accustomed to having strangers become excited around them finally understand exactly what that feeling is like from the other side.

Because apparently there is one thing fame can’t cure:

Meeting the person you’ve had a crush on for years.