While HBO has chosen to announce Christina Aguilera and Eminem's involvement, it apparently reserves the 'Twilight' star as a surprise guest.
There's a word buzzing around out there that Robert Pattinson is a guest star on the season finale of "Entourage". This is a curious case if it's proven true because HBO has been keeping it as a secret while in fact Pattinson's name could potentially lure additional viewers to the September 12 episode.
Pattinson, according to eWorldPost and TV Spreadit, is guest starring as Ari's most difficult client ever. Now, apart from the silence from HBO, IMDb and other reliable sites have not mentioned his name in the line-up but then again, Christina Aguilera and Eminem who have been confirmed by the network to appear in the finale, are also not listed.
The synopsis from HBO is not hinting any Pattinson either. It says, "Mrs. Ari is still fuming over Ari's angry meltdown the night before, Ari tries desperately to keep her surprise party on track. The guys attempt to stage an intervention for Vince, who has gone off the deep end. Turtle scrambles to find investors to save the tequila business. Eric receives an unexpected request from Terrance McQuewick, which leads him to consider Scott's business proposal."
In conclusion, it's possible that Pattinson is a well-kept surprise from HBO and the actor is made one of the guests in the party. After all, exec producer Mark Wahlberg did consider to bring the actor over, saying "Yeah. We'll see about that."