Britney Spears may be lip-syncing during her new tour...and the world has been reminded of why.

A retro video of Britney Spears singing in 2001 has gone viral [WATCH BELOW]. The video isolates Britney's microphone-and reveals how terrible her singing was.

It's not the most pleasant reminder-but it's pretty hilarious. The notoriously bad performance is full of off-key vocals to the songs "Boys" and "Lucky".

The notorious 20011 performance was live for HBO. Now, Britney will have a two-year engagement in Vegas...and fans are hoping history doesn't repeat itself.

Apparently, so does Britney, as she's been accused of lip syncing before the shows in her 'Britney: Piece of Me' show at Planet Hollywood have even started.

However, an insider said that it isn't true at all-and that Britney will phone it in with a lip sync sesh every performance.

The insider said: 'At the moment, she's set to pre-record vocals to use on stage rather than sing live.'

The source added: 'We have been given a sheet which gives answers to questions that potential customers and such may ask when they book, like whether or not Britney will be singing live ... The answers are twisted and far from the truth.'

A different source disagreed, though, saying, , 'She is being paid a lot of money to lip-sync. Her fans are none the wiser, but it is disingenuous of her to take their cash and not deliver a proper performance.'

Britney herself said she will sing live. She denied the lip sync rumors, telling Chicago's 103.5 KISS FM earlier this month: 'I'm definitely going to be singing live. I always sing live. It doesn't sound so great all the time, but I do my best.'

Watch the video below and let us know what you think-if the performance is that awful, maybe Brit SHOULD lip-sync?