You understand that the Michael C Hall is producing this stuff? He wants to bang Yvonne Strahoski. So he hires her to the show. Then he orders scripts that let him sleep with her. Just look at last nights episode. I haven't seen a girl spread her legs so wide in years. Michel really got his wish.
I assumed it was pretty established. Ivan talking about his unnamed son earlier in the episode (how he last showed compassion and love to his son right before he sent him away) and then Ivan going into Viktor's apartment and finding a secret picture of both Ivan and Viktor together.