Britney Spears Giving Free Concert in Mexico City on Sunday

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Officials expect 50,000 to attend the event, which will kick off the city's $2.6 million Christmas celebrations.

Britney Spears will follow up a Femme Fatale tour stop Saturday night in Mexico City with a free concert Sunday at the city's Monument to the Revolution.

Fifty thousand people are expected to attend the event, which kicks off the Mexican capitol's $2.6 million Christmas celebrations, notes the Los Angeles Times.

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Spears wrote on her Tumblr page, ”I’ve had so much fun and received so much love from my fans all over the world while performing my Femme Fatale tour which I am grateful for. I want to return some of that love so I’ve decided to give my fans in Mexico a special night and perform my Femme Fatale show for free,” says Britney.

The Femme Fatale tour has hit Venezuela and Guadalajara, Mexico, and moves on to Monterrey, Mexico, Santo Domingo in the Dominican Republic and Hato Rey, Puerto Rico in the next week.

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She took a break from the road for a quick trip to Houston on Friday to celebrate her 30th birthday with boyfriend -- and star of her "Criminal" video -- Jason Trawick.

Famous friends and industry peers like Nicki Minaj, Kim Kardashian, Katy Perry, Miley Cyrys, Heidi Klum, Kesha,, Christina Aguilara and Justin Bieber sent birthday greetings to the pop princess.

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Kardashian tweeted, "Welcome to the 30's club @BritneySpears Love you!." She also included a link to her celebuzz page that had the message, "Happy birthday to the beautiful Miss Britney Spears! Welcome to the 30’s club, Brit!! I wish you all the best for this next year and beyond. You’re going to love your 30’s! I love you and hope you have a magical day. Xo."

Minaj tweeted a video message, "Happy Birthday to a fellow SAG & beautiful ICON @britneyspears (its a video!!!!) :p

Bieber gave a "happy birthday shoutout" to Spears via Twitter.

Lance Bass was another of Spears' well-wishers. She wrote in a reply to his birthday Twitter message, " Thank u Lance for taking the time to make the video. You knew me when I was celebrating my 18th! Wow. Feels like yesterday. Xxoo