The Welsh opera singer broke down after performing a waltz with partner Mark Ballas as part of the Most Memorable Year week, with Katherine choosing 1996, the same year her father Selwyn died of lung cancer at the age of 70.
Visibly choked, Carrie said: ''It's like your father's arms were around you.''
Len added: ''The bottom line, you are a wonderful dancer.''
Speaking about the life-changing event, Katherine said: ''In 1996 we found out my father had lung cancer. I got pulled out of class by my auntie who said, 'Your dad's gone into a coma and gone into a hospice.
''It happened so quickly. The following day, he passed away and I'm just and I'm glad I got the chance to say goodbye.''
Katherine was not the only person to cry - 'The View' presenter Sherri Shepherd also wept as she talked about the premature birth of her son Jeffrey; she went on to score 24 out of 30 for her rumba with partner Val Chrmerkovskiy.
Meanwhile, William Levy and Cheryl Burke enjoyed a good week, scoring 28 out of 30 for their salsa based on the year 1995, when he went to the US from Cuba.
He also gained loud applause when he took off his shirt.