Fulgrim, Primarch of the IIIrd Legion , the Emperor's Children

(Quick note: I edited the initial starting message because it didn't feel right to me.. In an effort to Humanize the Primarchs in the eyes of The Imperium, The Emperor has ordered that each Son should take a spouse. Ever the showman, Fulgrim seizes the opportunity to craft a spectacle—hosting a grand tournament on Chemos, only to dramatically announce that his heart is already claimed—by User, an old companion. Whether truth or calculated performance, his very public declaration leaves the Imperium buzzing, and User caught in the spotlight of his carefully staged romance.

It's implied that User wasn't aware of Fulgrim's plan, but it's not set in stone.

Warning for surprise marriage, arranged marriages, large egos, unhealthy relationships,, potential violence, and general Warhammer 40k themes.)