Rihanna invites ex Chris Brown to her big birthday bash.

As Rihanna spent Valentine’s night with her ex, Chris Brown, are they officially getting back together?

It’s the news her fans have dreaded: Rihanna spent Valentine’s night with her ex, Chris Brown, Mirror reports.

In the wake of rumours that the pair have patched up their differences – the fact he beat her senseless in February 2009 being one fairly major difference – the Bajan star invited Chris to her pre-birthday party in a Beverly Hills mansion.

Tag-teaming with fellow single girl about town Katy Perry, RiRi worked the room where the With You star and a bevy of eligible young men were partying hard.

And post-divorce from Russell Brand, Katy, 27, was also up for fun.

One guest, Katia C, tweeted: “If Cupid was here he would be very happy everyone @Rihanna bday party was coupled up.”

She added: “All I can say, CB was invited and she [Rihanna] was acting like the happiest girl on her birthday and probably got what she asked for.”

There was no expense spared at the lavish do, where guests included Bruno Mars and Kelly Rowland.

RiRi had eight gold methuselahs of champagne on hand and kept revellers sated with 200 cupcakes (decorated to honour the star), mermaid vodka ice sculptures, a full Caribbean banquet and 150 of her favourite Cuban cigars – at £35 a pop.

I’m told: “Rihanna and Katy had everyone going crazy. By the end of the night they started a cake fight and were dancing together while Bruno and Chris looked on open-mouthed, cheering.

"RiRi made sure Chris was having a good time but then he kept a low profile, spending most of the night in a corner with a few pals.

“At one point Katy danced so much she broke her heels and had to leave the party barefoot,” adds my insider.

“Rihanna also had her own wardrobe casualty when her corset came undone but she didn’t let that stop the fun.”

This was the first of several bashes Rihanna, who turns 24 on February 20, intends to hold before she jets to London for next week’s Brits.

At the Beverly Hills party, RiRi was spoilt rotten with gifts including diamond earrings from Beyonce and Jay-Z… and a diamond-and-gold encrusted whip from another guest. Very kinky.

Meanwhile, Chris chose to hit out at the “haters” who complained that a woman-beater was allowed to perform at Sunday’s Grammys.

He tweeted: “Right before the world’s eyes a man shows how he can make a Big mistake and learn from it but still has to deal with day to day hatred! You guys love to hate!!! But guess what???

“HATE ALL U WANT BECUZ I GOT A GRAMMY Now! That’s the ultimate **** OFF!”

Sensibly, he later deleted the tweets.