Seymour realised she was shooting new TV movie Perfectly Prudence near Mackinac Island in Michigan, where she shot Somewhere in Time with the late Christopher Reeve - and she treated the cast and crew to a trip to mark the film's anniversary.
The visit inspired her 29-year-old daughter to surprise mum by showing up at a reunion party as her old character Elise McKenna.
She explains, "A few weeks later, Katie and (boyfriend) Brett dressed up like me (and Christopher Reeve)... with Christopher Reeve's actual vest from the actual shoot."
The actress' child by her third husband David Flynn plays her daughter in the film and Keach plays a businessman.
And Seymour reveals the writer penned the screenplay after spending time with the family.
She says, "The producers and the writer had met Katie... at my house and just thought what a great dynamic to have my real daughter play my daughter."
After two new producers are sent to help Prudence revamp her television show, in the process she rekindles a love she thought she lost, protects her daughter from the wrong man and ultimately finds a way to keep her show running on the right track.