When Alexandra's conception was announced, Allen Mackery merely smiled and counted backwards. A birth date in September meant that the child had to have been conceived in January. He didn't need Elizabeth to tell him the significance of that. But he said nothing, and gave no indication that he thought anything of it. He kept his head down, kept working, managed Hachiko and fulfilled his duties as Elizabeth's assistant. For the few press conferences where his presence was required, his portion was brief: all they wanted was a quick word, just a sentence from a businessman's standpoint. He performed his part beautifully.
During this time, the time between the public confirmation and the labor, he knew that Catherine was considering him as the father of this illegitimate child, but ultimately dismissed the thought. Allen was never told why he was dismissed, precisely, in the same way he was never told why he was a candidate. All he did was exactly what everyone else did: he watched, he waited, he expressed his congratulations.
Elizabeth never mentioned her child to him, except when her responsibilities as an expecting woman or mother conflicted with her duties as a chairman, a CEO, a boss. He followed her lead, and they never spoke privately about the daughter that nearly ruined everything. Indeed, after she announced her pregnancy, they never freely spoke to each other again. He had a ballpark estimate of her feelings on the matter, just as he had a ballpark estimate of the affluence of the underground organizations that Elizabeth so favored. And, just like those organizations, he had no definitive statement, nothing that was in no unclear terms.
Frankly, he preferred it that way.
And, when he came to the moral question of sleeping with a married woman, he explained to himself that it was mere morbid curiosity that led him to her bed. He wanted to know if she really did have cold eyes when she woke up after sleeping with a man. Their relationship returned to the way it had always been, and he was quite content. The future held everything he could play for.
Then her world crashed. The paparazzi, the reporters, the tabloids, the press, the people who wondered what kind of woman would marry such a wonderful man and then cheat in the first year of marriage. Allen merely stood aside and let the insults fly through the air past him, let them continue on their path to her, and did not once attempt to quiet the rabble. She would never have trusted him again if she believed that he he didn't trust her to handle this situation on her own.
He only saw the daughter, Alexandra, a handful of times before the pair of them left for Japan. After that, it would be quite a while before he saw Elizabeth. And he would never see Alexandra again.