Ex mother in law comes to visit

This guy says to his buddy, "You'll never believe what happened last night."
"Why?" his buddy asks. "What happened?"
"Last night the doorbell rang, and when I opened the door, there was my ex-mother-in- law on the front porch. She asked me, 'Can I stay here for a few days?'"
"Wow," says his buddy. "What'd you tell her?"
"I said, 'Of course, you can,' and shut the door."