The defense called the former Governor's youngest sister to the stand Tuesday in week four of the McDonnell corruption trial.
Her name is also Maureen but she goes by 'Mo' to her family.
Mo believes her sister-in-law felt 'trapped' referring to the governor's mansion as that 'prison mansion'.
McDonnell's sister also told the court she has seen Maureen hide things from Bob and try to work things to her benefit.
It's testimony that the former Governor says isn't easy to hear, but is a big part of the defense's case.
"It's very difficult. No one likes to talk about their marriage in front of the entire country but this is part of the case," McDonnell explained.
The former Governor and First Lady are accused of accepting loans and lavish gifts from Star Scientific CEO Johnnie Williams.
Prosecutors say the couple helped Williams promote his dietary supplement in return.
They worked together as part of a corrupt agreement, according to prosecutors.
But, Defense attorneys say Mr. and Mrs. McDonnell couldn't have conspired together because they were hardly on speaking terms when they met Williams.
Mo's testimony Tuesday may have strengthened the defense's argument that her brother's marriage was 'broken'.
A former special assistant to the First Lady also testified that Mr. McDonnell 'tuned her out' when Maureen took her anger out on him.
Another hot topic for the defense in the past two days has been how much money the McDonnells had in the bank when the allegations are said to have happened.
Defense attorneys called expert witness John Kosowsky to the stand to testify to that.
Kosowsky analyzed financial, bank and credit card statements for the McDonnells.
Witnesses have previously testified that Maureen told them her and her husband's credit cards were 'tapped out' and they were considering filing for bankruptcy.
But, according to Kosowsky the McDonnells still had more than $170,000 in credit available as of May 1, 2011- the same month Williams gave them the initial $50,000 loan.
Kosowsky said the couple also had nearly $13,000 in cash available during that time.
The defense hopes this testimony will prove the former Governor didn't need the loans and that Williams was just a generous friend.