The unstoppable Now That's What I Call Music series has claimed another victim.

This time, Vol. 7 of the killer album series has rolled over the world's biggest boy band, knocking 'N Sync's Celebrity down to the No. 2 slot on album-sales charts. 

Celebrity also saw a whopping 80 percent drop-off from its first-week sales, with 188,000 units sold. 

"When you open so big, you have no where to go but down," says Billboard charts guru Geoff Mayfield, noting Celebrity has sold a remarkable 2.3 million albums in two weeks. 

Now 7 sold 620,000 in its first week out, according to SoundScan, which tabulates retail sales. 

The hits compilation includes tunes from Janet Jackson, Eve and Gwen Stefani, Britney Spears and other chart busters — including 'N Sync's "This I Promise You." 

The Now series has been a smash hit overseas for decades and only began here in 1998. The fourth in the series, released in July 2000, was the first compilation ever to hit No. 1 on the top album charts. 

Albums in the Now series, which are released approximately every four months, regularly make their debut in the No. 1 slot and hover at the top of the chart for weeks. 

Now 6, released in April, still sits at No. 40, with a total of 2.9 million albums sold.

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