• Rapper Iggy Azalea With Singer Britney Spears

Rapper Iggy Azalea With Singer Britney Spears (Photo : Twitter)

Britney Spears, 33, and Iggy Azalea, 24, have started shooting the music video for "Pretty Girls." With a combined five number one Billboard Hot 100 songs under their belt, the pop stars are expected to top the charts with their collaboration song.

On April 10, Saturday, Spears and Azalea were spotted in their 80s looks in Studio City, Calif., for the filming of "Pretty Girls" music video, Just Jared reported.

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Spears took to Twitter to share a photo of herself and her dancers with a caption, "Just shot one of my favorite dance scenes ever with these boys!!"

It has been four years since Spears had a song that ranked number one on the Billboard Hot 100 chart. In January 2011, her dance track "Hold It Against Me" debuted at number one, making her the second artist to launch a song atop the chart several times.

In 2009, Spears single "3" from her "Singles Collection" ranked number one. Interestingly enough, the song is 3 minutes and 33 seconds long and it was her third Billboard Hot 100 number one song.

Spears' first Billboard Hot 100 number one song was her debut single "Baby One More Time," which stayed on top of the chart for two weeks in 1999. She was only 16 at the time. It took her nine years to have another chart-topping song. In 2008, her "Womanizer" ranked number one on Billboard Hot 100.

On the other hand, Azalea's first and only Billboard Hot 100 number one song so far is her 2014 collaboration song with Charli XCX titled "Fancy." It stayed at number one for six weeks making it the longest-leading number one song by a female rapper, according to Billboard.