"Castle" season 8 actor Nathan Fillion gave tribute to the on-screen women in his life for the success of the ABC series, but he's coy about the exit of Penny Johnson Jerald.

Apart from Kate Beckett (Stana Katic), there are two other women in Richard Castle's life: his daugther Alexis (Molly Quinn) and mother Martha Rodgers (Susan Sullivan).

In an interview with TVGuide, he credited the two actresses for adding to the ingredient that makes "Castle" a success.

He said, "All you want is for them to come into the room and just be exactly what you're looking for and that's exactly what Molly did. She came in and was phenomenal. She left, the door closed and we picked up the phone and said 'that's her, we need her, it's a done deal.'"

"It was the same thing with Susan," Fillion said. "She has so much of Martha in her. She came into audition and said, 'stand up darling, I won't be looking down on you, that won't work for me.' She had me stand up and read with her and that's just so Martha."

However, Nathan Fillion was silent on the exit of Penny Johnson Jerald in the season 8 of "Castle," whose character Capt. Victoria "Iron" Gates had as much influence on Rick.

Screenrant reported that Penny Johnson Jerald won't be reprising her role after joining the series as a regular back in "Castle" season 4.

"Captain Gates was still alive at the close of season seven, there's no telling how or why she will ultimately leave the NYPD's 12th Precinct," it said.

But it turned out that the news of her departure from "Castle" season 8 came as a shock to Penny Johnson Jerald who learned of the announcement at the same time with fans around the world.

In a Twitter post, the actress wrote, "To my Castle fans around the world, as of late yesterday I am surprised and saddened to learn that I will no longer be a part of the Castle family. Thank you all for your support and love. Hugs from PJJ."