Wait...Gertrude and Claudius weren't seeing each other while King Hamlet was still alive were they?
I read something saying that the reason Claudius killed King H is b/c he wanted Gertrude for himself which is certainly true but they also said that Gertrude was sleeping with Claudius from the very start, making his decision to kill King H very easy.
Shakespeare does not explicitly come out and tell us whether or not Gertrude and Claudius were having an affair while Hamlet Senior was still alive. But I would infer from things in the play that they were not.
First of all, the ghost never says that Gertrude committed adultery, just that Claudius did. How can this be? If you go by the part in the Bible where it says that just lusting after someone can be adultery, this makes sense. Maybe Claudius really wanted her but she didn't want him at that point.
Second, Claudius says he killed his brother so he could become king and so he could have Gertrude. If he already had her, why would getting her be part of the reason for killing Hamlet Senior.
Neither of these is proof, but I think they both point toward the two of them not actually having an affair.
You can't believe everything you read, especially in gossip sheets about fictitious Shakespearean characters.
Of course, since Gertrude was the wife of Claudius's brother, Gertrude and Claudius no doubt knew each other for years. There is no way to know, however, whether they lusted after each other during that time. And, as said above, the Ghost who, from his vantage point, might be privy to such matters, makes no accusations of a previous relationship between the two. Nor does Hamlet's play-within-a-play suggest such hanky-panky.
Indeed, the only thing that would make anyone suspicious of any pre-murder betrayal would arise from the player queen who speaks very very lovingly of her husband, to which Gertrude, the real Queen responds, "The lady doth protest too much, methinks."
Hamlet does call Claudius an "adulterous beast," but I don't think this implies that Claudius and Gertrude were having an affair while the king was still alive. The Ghost blames Claudius completely, saying he seduced his queen but the Ghost does of course hold a grudge against his queen. The Ghost's language makes it seem like there was something going on while he was still alive, but this is because the Ghost is still a part of this world, in a kind of purgatory. Since the Ghost is still around, bearing witness to Claudius and Gertrude's relationship, it is as if, from his (Ghost's) perspective, he is still alive. So, the Ghost's language might infer that he 'is being' betrayed, when in fact, he was not betrayed by Gertrude until after his death (albeit too soon after his death).
Also, the Ghost tells Hamlet not to harm Gertrude: vengeance is marked only for Claudius. Gertrude's penance is that she must deal with her conscience. Most evidence points to Gertrude being shallow and a bit naive, but at times she is portrayed as inherently good in wishing for the well being of those around her: particularly Hamlet and Ophelia, but also Claudius. She takes too long to see what's going on, but there are too many hints that say she was not involved in the plot.
In ACT III, Scene iii, Claudius says:
"Of those effects for which I did the murder,
My crown, mine own ambition and my queen.
May one be pardon'd and retain the offence?"
This could be the order of his plot, the seduction of the queen being last, implying the queen was not involved and they were not having an affair until after Claudius had killed the king and achieved the crown.