18 May 2009
Miss Washington admitted she was having an affair when she conceived, when two eggs were fertilised by the sperm of two men.
"I have twins, but they're by different fathers," said Miss Washington told Fox News.
Miss Washington and her partner James Harrison took DNA tests after noticing twins 11-month-old Justin and Jordan, had different facial features.
"Out of all people in America and of all people in the world, it had to happen to me. I'm very shocked," Miss Washington said.
According to the paternity test, there's a 99.999 percent chance Justin and Jordan do not have the same father, and zero percent chance they do.
The lab claims it has never seen this type of result, nor do they expect to see it again.
"It is very crazy. Most people don't believe it can happen, but it can," said Clear Diagnostics President Genny Thibodeaux.
Only a handful of cases - of what doctors call heteropaternal superfecundation - are documented in the world.
Dr Chris Dreiling said the conception can happen when a woman releases multiple eggs during ovulation. If she has more than one sexual partner within the same time period, sperm cells can fertilize two separate eggs.
"This is likely to be the only time that we will ever see this occur in the city of Dallas; it's that rare," said Dr Dreiling.
The twins' father said he's forgiven his fiancÚ's infidelity and has vowed to stay with her and raise both boys as his own.
"It's a day by day thing. It's going to take time to build that trust like we had," said Mr Harrison.
Miss Washington, from Dallas, Texas, said she plans to tell the boys about their DNA differences when they're old enough to understand. But she says she has no plans to tell the other father.