And that's Stan-level canon, folks. In fact, she looks so much like Sue that a blonde wig can fool her own brother who's known her for 16 years:
And it takes even Reed quite a few minutes (admittedly, some very busy minutes where the Thing is busting names and taking heads) to realize that ain't Sue:
This and previous panels are from Fantastic Four #8 (November 1962), script by Stan Lee, pencils by Jack Kirby, inks by Dick Ayers
So. Keep that never-again-mentioned fact in your head: Alicia Masters looks pretty much like Susan Storm.
Flash forward many-Marvel years, during which loverboy The Thing has been dating and romancing Alicia, but has now been left behind on a distant planet in another galaxy (whatta revoltin' development!). And guess who's makin' time with Mister Grimm's girl?
Panel from Fantastic Four #270 (September 1984), script, pencils, and inks by John Byrne, colors by Glynis Wein, letters by Michael Higgins
Smooth move, flamebrain! Not merely moving in on your best pal's girl...but being attracted to a girl who, give or take a blonde wig, looks...as we've mentioned...just like your own sister. Johnny, no!
Panel from Fantastic Four #276 (March 1985), script and pencils by John Byrne, inks by Jerry Ordway, colors by Glynis Wein, letters by John Workman
That ain't creepy at all, is it? Well, at least it's just a little huggin' and kissin'...with a girl that looks just like your own sister, Johnny. It's not like it's going any further, is it?
Panels from Fantastic Four #277 (April 1985), script, and pencils by John Byrne, inks by Jerry Ordway, colors by Glynis Wein, letters by John Workman
Oh, those boys...they just love the roughhousing! Well, after all the rubble settles and Johnny gets out of traction, that's pretty much it, isn't it? I mean, it's not like it's anything more than just a little fling with a girl that looks just like your own sister, Johnny, right?
Panel from Fantastic Four #300 (March 1987), script by Roger Stern, pencils by John Buscema, inks by Sal Buscema, colors by Glynis Oliver, letters by John Workman
D'oh! Johnny, no!
Well, it all works out in the end, when Alicia turns out to be a Skrull. Well, that'll happen. Mind you...a Skrull that can look just like your own sister, Johnny.
Panel from Fantastic Four #357 (October 1991), script by Tom DeFalco, pencils by Paul Ryan, inks by Danny Bulanadi, colors by Christie Scheele, letters by Bill Oakley
Thankfully, that's all in the past and is pretty innocentit's no worse than Professor X being in love with his teenage student in X-Men #3, is it? (Don't answer that.) But that's the only family member Johnny ever felt romantic towards, right?
Panel from Strange Tales #103 (December 1962), plot by Stan Lee, script by Larry Lieber, pencils by Jack Kirby, inks by Dick Ayers, colors by Stan Goldberg, letters by Art Simek
Geez, Johnny, no!