Lady Sif will appear in episode 15 of Marvel's Agents of S.H.I.E.L.D., Image source: Disney/Marvel

If you've ever wished Disney (DIS 1.50%) Marvel's Agents of S.H.I.E.L.D. was just a little more Marvel-ous, you're gonna love this.

During ABC's Television Critics Association winter press tour Friday, ABC President Paul Lee revealed Thor: The Dark World's Jaimie Alexander will appear as Lady Sif in episode 15 of Agents of S.H.I.E.L.D. 

Why this is a huge deal
You can guess how I feel about the announcement considering I've already rallied for Lady Sif to appear in her own movie -- but I also know I'm not the only one excited for the Asgardian warrior to appear on the small screen.

And no, this won't be a minute-long cameo like we saw earlier this season with Samuel L. Jackson as Nick Fury. To the contrary, Lee insists Lady Sif's role will be "absolutely integral to that hour of television." In addition -- and perhaps hinting at another big crossover -- Lee promised Agents of S.H.I.E.L.D. viewers they'll know who the Clairvoyant is by the end of the season, and that "it's going to be very, very cool."

So why else is this is a big deal? In short, it represents a much more significant movie crossover than the one we saw in November, which merely introduced a previously unknown Asgardian character while Coulson and his team handled the fallout of Thor: The Dark World.

The funny thing is, that crossover ended up resulting in the show's strongest ratings performance in eight weeks, gathering 6.89 million live viewers and a 2.4 rating for the key 18-49 demographic. In the end, you can bet that raised some eyebrows by validating Disney's broader strategy of combining characters from the same universe across different entertainment mediums.

Ratings are heating up
But keep in mind we're also talking about episode 15, which means fans will need to wait an entire tantalizing month since episode 13 is scheduled to air on Feb. 4. However, that should also give the show plenty of time to stir up hype surrounding Lady Sif's appearance, which could easily provide its biggest ratings boost yet.

So how's Agents of S.H.I.E.L.D. holding up right now? Pretty well, actually.

Live ratings for this week's show held steady at a 2.2 in adults 18-49 with 6.37 million viewers. That earned it a solid second place behind CBS' (PARA 3.55%) Tuesday ratings juggernaut NCIS, which scored a 3.0 rating with an incredible 19.72 million live viewers.

That may not sound too impressive on the surface, but remember Agents of S.H.I.E.L.D. once again dominated the valuable men's 18-34 demo for the 12th consecutive episode this week -- leading NCIS in the category by 50%, by the way. At the same time, Agents of S.H.I.E.L.D. stood as the top-rated broadcast program with both teens 12-17 and kids 2-11.

Finally, Agents of S.H.I.E.L.D. is still Tuesday's number-one show this season so far with a 4.6 rating based on the most recent live+7-day numbers. For reference, NBC's The Voice currently stands second with a 4.5, while CBS' NCIS remains a distant third at 4.1.

In the end, that explains why Lee also felt comfortable saying ABC feels "very, very good" about both the show's creative and ratings stability, and that he expects its to stick around "for a very, very long time."

So stay tuned, Marvel fans, because I think the best is yet to come.