Jul 1, 2009, 5:00 GMT
Justin Timberlake jammed with Guy Ritchie on Monday night (29.06.09).
The 28-year-old singer rushed to Madonna's ex-husband's London pub The Punchbowl after enjoying a late dinner at The Wolseley.
After greeting each other with a hug, the pair - who became friends when Justin worked with Madonna on hit single '4 Minutes' - downed pints of lager, before dusting off a banjo and a guitar and belting out a few songs.
An onlooker said: "Justin got there about 11.30pm. Guy had been there since 8pm and the night quickly got very merry. At one point they were in such high spirits, Guy picked up a banjo and handed Justin a guitar and they had a little singsong."
Justin - who is dating actress Jessica Biel - left the pub at around 1am, and headed to a private party in Mayfair, before returning to his hotel at 2.30am.
Justin has been linked with starring in a tribute concert to Michael Jackson - who died of a suspected cardiac arrest last Thursday (25.06.09) - but admits he would be "cautious" about taking part.
The 'SexyBack' singer told London's Evening Standard newspaper: "It is extremely tragic - there really was only king. It's an honour to be considered for a tribute to the greatest of all time but also there is a level of just me as a fan that would feel very cautious about doing something like that.
"Like anyone else in the world I'm his biggest fan. I just feel like if there would be any pretension, it would not be good. That's my worry. I understand tributing somebody who is so influential to every artist of our generation. It would have to be done properly."
Concert promoters AEG are said to be trying to organise a series of concerts to fill some of the dates allocated for Jackson's 50-date residency at London's O2 Arena, which was due to begin later this month.
In addition to the 'Like I Love You' star, they are also reportedly trying to recruit Diana Ross and Ne-Yo.
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