According to Wikipedia's "On this day..." section:
1533 – Anne Boleyn, already pregnant with future queen Elizabeth, secretly married Henry VIII of England, the second of his six marriages.
What's the evidence that she was already pregnant? Elizabeth was born on September 7, which is about 8.5 months after the wedding. I'm no doctor, but that seems like a totally reasonably gestation period if she conceived on the wedding night (January 25).
And presumably if Anne knew she was pregnant before the wedding she would have had to conceive over a month previously, which means the gestation was over 9.5 months, which seems too long.
So what's the verdict? Is Wikipedia just speculating or was Elizabeth in utero for 10 months? Or am I looking at this totally wrong?
Okay, the tricky thing here is that Henry and Anne had two weddings. Their first, secret wedding was soon after they returned from Calais, at the end of 1532 (I can't seem to find an exact date in any of the sources I have to hand, sorry, I'm not sure if the exact date is known). To fully legitimise their marriage (his marriage to Catherine of Aragon wouldn't actually be ruled invalid until May 1533), they married again (also privately) on 25 January 1533.
If Elizabeth was born on her due date (for the sake of argument), the first day of Anne's last period would have been December 1st and the baby would have been conceived mid-December. Therefore, it is entirely possible that Henry and Anne consummated their relationship after their first marriage, Anne missed a period at the beginning of January, and they had their second ceremony when it became clear that her period wasn't just a little late. Remember, Henry had been waiting years for a son, and had been chasing Anne for six years by that point.
Also, I think the math is a little off -- January 25th to September 7th is 7.5 months, not 8.5. Technically possibly viable, but at the time would have probably been much more cause for concern if a child was born so early.
So the answer to your question is, it is conjecture whether or not Anne knew she was pregnant when she and Henry married the second time, but it's certainly possible, and even likely.