Nicholl says Harry saw it as criticism and interpreted it as William not being "behind" the marriage. "And I don't think things have been quite right ever since," Nicholl says above.
But Lady Colin Campbell, a royal biographer, says any distance between the two royal brothers is likely because of Meghan's influence.
"Everything I hear is that Harry is completely beguiled by Meghan, and completely enthralled to her and has changed considerably," Lady Campbell says in the exclusive clip.
The clip above also features commentary by Ingrid Seward, the editor of Majesty Magazine, who gives her insights on the rumored division between the "fab four."
Kate v. Meghan also features commentary from Paul Burrell, the former butler to Princess Diana, CNN's Victoria Arbiter, a body language expert and more.
Kate v. Meghan: Princesses at War? airs Tuesday, Feb. 5 at 10 p.m. on TLC.