Uncovering the New "Her" Mystery on This Is Us: Who Is Kevin's Fiancée in the Flash-Forward?

When Jennifer Morrison was first cast on the series, one of the first theories fans had is that she would be playing Kevin's love interest and the eventual mother of his son in the future. While Cassidy seems very adamant about getting her life together so she can return to her own husband and kid, she does have a brief fling with Kevin. Seeing that Kevin's 40th birthday takes place around nine months later, it's possible that she eventually gets pregnant and Kevin proposes.