Charlie Sheen has blasted John Mayer for suing his friend.

The singer-songwriter filed a lawsuit against Robert Maron, accusing the jeweler of selling him a counterfeit Rolex watch after he splashed out $5 million on several timepieces, but Anger Management star Charlie believes John knew the accessory wasn't authentic and claims he also re-sold a number of counterfeit designer watches for a huge profit.

"WAIT!! Mayer spent $5M with Maron and is crying about $600K?!? Ask him how he did on the $4.4M...! Sorry that seven of your 100 watches aren't to your liking! boohoo!!" the 48-year-old actor told gossip website TMZ.com.

Maron's lawyer, Eric George, claims he has proof that John, 36, is lying about claiming he didn't know the piece had counterfeit parts because the "Who You Love" hitmaker allegedly expressed an interest in buying a fake Rolex Flat Dial on a message board in 2007. The star is quoted in a letter as saying, "Anyone who wants to sell me one of these watches can get these fake pieces off their hands and make a killing on it. I will even accept a letter from you as a dealer releasing you from any liability in having sold me a counterfeit dial. I will be buying these as counterfeits."

Charlie, who also collects Rolexes, added, "Maron wrote the book - period the end. Nothing but respect for Bob -- his integrity is beyond reproach! This calamity of buyer's remorse seven years after the fact is clearly a reflection on John Mayer's character and not on Bob Maron's."

John claims he was shocked to find one of the timepieces was a replica after sending it for repairs three years later. He reportedly returned the watch and was given credit to buy another but now wants a refund for $656,000 he spent on seven other watches which Rolex have told him are counterfeit.