'Britain's Got Talent' panel has been together 10 years - who else has judged the show?

Britain's Got Talent is unique in the world of reality TV for having a judging panel that hasn't changed in 10 years.

It's almost unheard of for the same line-up of judges to keep returning to a series for so long, but the ITV talent show seems to have struck gold in its casting as over the weekend, its four stars celebrated a decade working together.

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Simon Cowell, Amanda Holden, Alesha Dixon and David Walliams are clearly enjoying each other's company, no matter how much they like to play up rivalries for the cameras - but who has sat on the BGT panel before them?

All the Britain's Got Talent judging line-ups

Simon Cowell, Amanda Holden, Piers Morgan - 2007 - 2010

Cowell and Holden have been around since the early days of Britain's Got Talent, but for the first four series they were joined by controversial broadcaster Piers Morgan.

Despite the risk of that being too much Mr Nasty for one judging line-up, it worked strangely well while it lasted - until Morgan left to launch his US TV career.

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Back in those days, there were only three seats on the panel, although Kelly Brook was brought in as an extra judge for series three.

However, less than a week after she began, show bosses decided a fourth judge overcomplicated things and so she was credited as a guest judge instead.

Cowell's old X Factor pal Louis Walsh also debuted as a guest judge in series four when Cowell fell ill and couldn't attend some of the auditions.

Amanda Holden, David Hasselhoff, Michael McIntyre - 2011

The show's first big line-up change came in series five, with Morgan off to break America and Cowell hot on his heels launching The X Factor USA.

Holden was the only original panel member left holding the fort for the whole series, although Cowell did manage to return as a fourth judge in time for the live shows.

Read more: Simon Cowell denies he plans to retire from TV judging

In the meantime, Holden was joined by Baywatch star David Hasselhoff and comedian Michael McIntyre, although the combo was shortlived as both new signings didn't want to come back for series six.

Walsh was a guest judge again during one audition round, covering for Hasselhoff who was performing in a pantomime.

Simon Cowell, Amanda Holden, Alesha Dixon, David Walliams - 2012 - present

So began the latest and greatest line-up which has lasted since series six of Britain's Got Talent.

Cowell returned full-time to oversee the panel, Holden stayed on in her usual seat, and the show recruited Dixon and Walliams to join them.

Dixon had been a judge on BBC rival Strictly Come Dancing but was lured to ITV by Cowell, while Walliams rounded out the panel, making what had seemed like a strange job for a comedian when McIntyre took it on fit perfectly.

It's rare for reality TV to land a panel where the stars get on and have great chemistry, but they've managed it with this long-running cast.

There have been a few guest judge additions over the years - in series six, Carmen Electra covered for Holden for some of the auditions as she recovered from her daughter's birth.

Cowell has also had a few stand-ins, including hosts Ant and Dec covering a day of auditions for him in series eight, Walliams' mum Kathleen who was in the audience filling in when he was late to work in series 10, and former BGT winner Diversity star Ashley Banjo replacing him during series 14 after his electric bike accident.

Whether any of the panel will view the 10-year milestone as a good point to bow out remains to be seen next series...

Britain's Got Talent continues on Saturday at 8pm on ITV.

Watch: Ant McPartlin needed medical attention on Britain's Got Talent set