This is one of those things that we can really never know for certain. But, the incestuous nature of George and Anne's relationship was believed by many at the time and was an easy way out for Henry VIII.

As you know, Henry went through a LOT of trouble to put aside Katherine in favor of the younger (and hopefully more fertile) Anne. The need to have an heir was her sole job as Queen and after the birth of Elizabeth, followed by a few miscarriages, her need to have a male heir would have been imperative in order to truly secure her place. Much of the public didn't accept her as a true Queen and more of a concubine, but bearing a royal prince would have probably changed all of that for the better. Later wives of Henry VIII had similar issues with pregnancies, indicating that the problem probably lay with him. It's entirely possible that Anne thought as much and sought a pregnancy at any cost. Her brother would have been the most trusted person to keep that secret, if she had gone outside the marriage bed to conceive.

The last miscarriage was said to have been greatly deformed, necessitating the King to clearly define that it was not his issue. A monstrous child that was of his loins would have, perhaps, been viewed as a sign from God that he had done a really terrible thing by ditching the Catholic church and putting aside his wife. So, claiming adultery was a solid way to ensure that no one thought he could be the father of a deformed baby.

It didn't help that Jane, wife of George, allegedly testified that the affair had taken place. And though Anne could provide her whereabouts on all the occasions she was alleged to have committed adultery with a host of different men, her fate was sealed before the trial even began. King Henry VIII had already started planning his next marriage and executing Anne was the most expedient route to ensure he didn't have to face the enmity of his people with yet another divorce.

When we look at his subsequent treatment of his wives and how all of them were put aside in one way or another (with the exception of Jane Seymour), it seems fairly clear that Anne was probably innocent of the charges against her. Most historians agree that the trial was a farce and that the political maneuverings in the court were more at fault than Anne herself.

There are also some interesting studies on the possibility that Henry VIII was Kell positive, which would have created the same pregnancy patterns that we see in his lineage.

Allow me to speak on behalf of the dead and often maligned Anne Boleyn. I shall do it indignantly (but with cites). She was accused of sleeping with five men including her brother. The evidence consisted of evidence supplied by her 'lovers' after they had been tortured and some hearsay evidence from people like her brother's wife (later pronounced mad) . http://scholarship.law.wm.edu/cgi/viewcontent.cgi?article=2290&context and http://www.historylearningsite.co.uk/anne_boleyn.htm.

To be fair, some scholars claim she might have had affairs. Based on a poem they found. http://www.telegraph.co.uk/culture/books/booknews/7295739/Poem-provides-evidence-that-Anne-Boleyn-had-numerous-affairs.html. Other historians have noted that the executioner was sent for before the trial and the King married his mistress 11 days post execution. http://www.npr.org/templates/story/story.php?storyId=122872854. They also note there wasn't any real evidence produced, in fact, the men charged weren't allowed to defend themselves at all and had confessed after being tortured. The evidence at Anne's trial consisted of accusations, not evidence. Most agree she did not get a fair trial.http://www.britannia.com/bios/aboleyn.html

The actual reason Anne Boleyn was executed? Henry needed a male heir and Anne produced only a daughter and had had 3 miscarriages. She had to be gotten rid of just as he got rid of all his other wives who weren't able to give him a son. He knew that not having a son to succeed him could lead to another War of the Roses. http://education-portal.com/academy/lesson/henry-vii-the-kings-great-matter-and-the-succession-acts.html#lesson.

As it turned out, historians believe Henry Viii's lack of success in producing a healthy male heir had to do with his own health issues (http://www.nbcnews.com/id/42041766/ns/technology_and_science-science/t/king-henry-viiis-health-problems-explained/) so divorcing and murdering a variety of spouses didn't really help him out much.
So the body count thanks to Henry trying for a male heir comes out to three dead wives (two to execution and one to childbirth). There were also two divorces and one annulment. http://www.pbs.org/wnet/sixwives/meet/ On the bright side, we do get two plucky survivors of marriage to Henry. Anne of Cleves had her marraige annulled by Henry and strategically withdrew and led a happy, if quiet life unmarred by executioners. http://tudorhistory.org/cleves/ Meanwhile, Katherine Parr survived Henry and got to marry someone she actually liked. Ironically, Henry's son did not survive but his daughter Elizabeth was a very successful ruler and averted the civil war he feared.

The answer is - there is no answer as historians don't agree. When Anne Boleyn was accused of high treason for adultery, she was accused of sleeping with more than just her brother George Boleyn. (National Archive sources and more national archive sources) Henry Norris, Sir William Breretan, Sir Francis Weston, and Mark Smeaton were also on the list and specific dates were given of the alleged affairs and it was a few days later when George Boleyn was accused. The primary testimony at George Boleyn's trial was his estranged wife, Lady Jane Rocheford, and it's interesting to note that she was later executed by Henry VIII for her knowledge of Catherine Howard's previous relationships - and possible assistance with the continuation.

Now as for the accuracy of the claims in the trail- there is no real answer. According to the late Joanna Denny "Henry’s hand in the whole sordid business is clearly seen: the real blood-guilt lies with the King." On the flip side you have George Bernard who cites letter written by a French poet as proof of her guilt due to the various gifts she gave her favorites. However a few of the men have been "acquitted" of their crimes at least as far as the trial. As I mentioned earlier very specific dates were cited for the transgressions with the exception of her brother. Using household documents showing the progress of the court throughout the year historian Eric Ives was able to prove that on at least 12 of those dates (75% of those cited in the original court documents) Anne and the gentleman in question were in different places. That still leaves a few dates where she was in the same place - which is why there is still that small chance that they were right 25% of the time. Since no dates were associated with George's crimes and his wife's testimony is what damned him, chances are historians will never be able to say with 100% certainty if she did or did not sleep with him.

There are also a few historians that suggest the reason for George's later addition was his (alleged) homosexuality (Retha Warnicke) however none of the more modern sources cite that particular reason - although both Bernard and Ives include arguments against this accusation in both of their books. Another explanation worth including is 'The Cromwell Conspiracy', that essentially he engineered the entire thing in an attempt to save himself - which is suggested by Ives, Claire Ridgeway, and even Bernard (at times) but is never conclusively proven. Which worked until Henry VIII married Anne of Cleves as he was arrested on June 10, 1540 and executed July 28 of the same year. His letters to the king can also be found in the National Archives, and include letters from the time period of Anne's trial.

For a really interesting (IMHO) read check out the William and Mary Law Review for while it doesn't proclaim her guilt or innocent it does do a fantastic job of describing the trail.

All the defendants denied the accusations against them before and after sentencing, save Smeaton. Contemporary views were that it wasn't really possible that the accusations could have been true. The Imperial ambassador Eustace Chapuys said 'although everybody rejoices at the execution of the putain [whore], there are some who murmur at the mode of procedure against her and the others, and people speak variously of the king'. John Foxe couldn't believe that Anne was guilty of incest 'being so contrary to nature, that no natural man will believe it', George Wyatt (Anne's first biographer), considered the whole thing to be 'impossible', and George Constantyne recalled 'there was much muttering at Anne's death'.

So no, it wasn't true.

Did she have three breasts? I was told that on a tour in England.

What's your source for the claim?

Edit: Jesus Christ. I was only going to help him analyse the validity of his sources.