'How I Met Your Mother' Season 9 SPOILERS: John Lithgow Joins Finale Cast, Barney's Stepmother and Kids? Episode 4 "The Broken Code" Premiere Monday on CBS [TRAILER]

How I Met Your Mother Season 9 Spoilers!

The ninth and final season of How I Met Your Mother premiered two Mondays ago, which means Barney and Robin's wedding weekend is in full swing, with guests arriving.

As was reported earlier, Barney's dad John Lithgow will be making an appearance very soon. Fans of the CBS sitcom have met Barney's dad before. This time viewers will get to meet Barney's stepmother, Cheryl at the festivities leading up to the wedding. Cheryl's two kids will also be featured in the Season 9 cast.

When Lithgow will make his Season 9 debut is currently unknown.

As for news on the series finale, Ted's kids might have a little more information.

The actors who play Ted's future children, Lyndsy Fonseca and David Henrie confessed the show's ending was filmed long before the ninth season.

"We signed a confidentiality agreement saying that we would not say who The Mother is," Fonseca told TVLine. "They also didn't know how many years the show was going to go. They filmed the ending of the show then just to have it."

Fonseca said her and her co-star had to sign confidentiality agreements, swearing the two actors to secrecy.

"I don't even remember what I signed! I don't even remember what the secret was. David says he kind of does. So it's been this running joke between the creators and me," Fonseca said.

"I do remember. I think I remember. We'll see...My friends and my family are the worst," Henrie said, "[and] especially people at bars who try to get me drunk to get it out of me."

Well, those weren't exactly the spoilers I was hoping for.

Tune in to How I Met Your Mother Season 9, which airs Monday at 8 PM ET on CBS.

Here's a trailer for next week's episode "The Broken Code"