However, Big Bang Theory co-stars Kaley Cuoco and Johnny Galecki managed to pull off one

of the biggest secret relationships in Tinsel Town.

The stars, who play Penny and Leonard on the hit CBS sitcom, revealed in 2010 that they'd

been dating for around two years, but had split on friendly terms.

People were shocked — how could they keep it so secret for so long?

While Leonard and Penny are still in love and even walked down the aisle on The Big

Bang Theory, their real-life relationship fizzled out off-screen.

"You wrote vows?"

"Yeah."

"I don't have any, you're kinda making me look bad."

Let's look at the real reasons the secretive lovebirds ended their illicit romance.

Forced into hiding

After confessing to dating her co-star in an interview with CBS Watch! magazine back

in 2010, Cuoco also revealed that she never went anywhere with Galecki during their two-year

romance, for fear of being photographed together.

"This is the first time I've ever talked about it, ever.

It was a wonderful relationship but we never spoke a word about it and never went anywhere

together.

We were so protective of ourselves and the show and didn't want anything to ruin that.

But that also made it sad, too.

That's not the kind of relationship I want — I don't want to be hiding.

We couldn't do anything.

It wasn't as fun as we wanted it to be."

Penny and Leonard forever

Galecki opened up about the romance in 2013, and revealed how he and Cuoco were worried

their off-screen romance would distract from the on-again/off-again relationship their

characters Leonard and Penny had on The Big Bang Theory.

He told CBS Watch! magazine

"I just don't like to speak about it.

And not because I'm trying to be enigmatic; I just worry that it will conflict with people's

acceptance of Leonard and Penny…

I get the curiosity, but I don't want to distract from the story."

Despite their off-screen relationship ending, their beloved characters Penny and Leonard

ended up getting married in the first episode of season nine, which aired in September 2015,

and then wed again in season ten in 2016.

"I now pronounce you husband and wife.

And weird other husband who came with the apartment."

Lying to their friends

The cast of The Big Bang Theory are all good friends, as most of their behind the scenes

photos prove.

All they seem to do is goof around on set.

"That's fantastic, and you have real beer in the refrigerator"

"Oh, isn't that nice, we'll need that replaced."

"It's mine now."

But despite their tight-knit friendship with their co-stars Jim Parsons, Kunal Nayyar,

and Simon Helberg, Cuoco and Galecki still chose to lie to their friends about their

blossoming romance.

"We didn't tell them, for like four or five months, which was horrible because we were

like best friends then."

Eventually, it affected their relationship.

"Everyone was always asking, and we deny-deny-denied.

And I'm like, 'Why am I denying this person that I love?'

It took a little bit of a toll on me and I think it did for him, too…

We knew how to keep it deep inside and never bring it on that set, ever."

They even worked during the aftermath of their break-up without telling anybody on set that

they'd ended their relationship.

Said Cuoco about the breakup: "We broke up before the holidays and worked that whole

time.

We dodged a huge bullet.

Dodged a war."

Child star pressures

Cuoco started acting as a young child.

She was only ten when she appeared in the Denzel Washington sci-fi thriller Virtuosity

in 1995, while Galecki caught the acting bug when he was just six years old, and got his

big break at 14 when he was cast as Chevy Chase's son Rusty in 1989's National Lampoon's

Christmas Vacation.

"Russ!"

"Right here, dad"

"Huh, there you are."

Having dealt with the pressures of Hollywood longer than most, the two were desperate to

keep their romance away from the prying eyes of the paparazzi and celebrity gossip magazines.

However, it was a decision that ultimately ended their two-year-long romance.

As Cuoco put it:

"When you're dealing with two professionals who have been working since they were both

four — and who kept their lives extremely private — we didn't want anything other

than that."

A doomed romance

Despite their admiration and respect for one another after their break-up, Cuoco revealed

that the couple had actually agreed on how they would deal with ending their relationship

when they first began dating.

Cuoco told CBS Watch!:

"We knew we weren't destined to be together.

We accepted it and said, 'Look, if we ever break up, we will be professional.

I'm so lucky it was a mutual ending and that we don't hate each other.

We've seen that happen on other shows."

Better friends than lovers?

Since their break-up, the couple have continued to be close friends, even meeting each other's

partners and goofing around in interviews.

Were they just always destined to be better as friends than as boyfriend and girlfriend?

"We're going to put on music and dance in our underwear."

"Ugh, can't we just have sex?"

Galecki told The View that their professional relationship still works so well because they

still love and respect each other.

"It's not easy, but with those two ingredients, pretty much anything is possible and we're

dear, dear friends."

Rumors swirled that the pair were dating again after Cuoco split from her husband Ryan Sweeting

in 2015.

But the on-screen sweethearts took to social media to shut down the false reports.

Cuoco posted a shot of her and her former boyfriend on Instagram with the caption, "No

scandals/home wreckers/pregnancies here, y'all.

Just profound friendship."

Looks like we'll just have to settle for the on-screen romance of Leonard and Penny!

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