John Spencer (Leo) died 5 days after the airing of this episode.
In order to make room for other guest stars in this episode, the actors portraying President Bartlet's daughters Liz and Zoey, as well as the actors playing their significant others (Charlie and Doug), are conspicuously absent from middle daughter Ellie's wedding.
At the end of Josh (Bradley Whitford)'s and Leo (John Spencer)'s scene when the wedding is about to start, the music heard is not "Sorge nel petto" as Will (Joshua Malina) explains at the briefing, but "Lascia ch'io panga" - from George Frideric Handel's 'Rinaldo' also, but a bit less appropriate (with words that translate as "Let me weep over my cruel fate, And that I long for freedom!") - unless the scriptwriter(s) had a gloomy view of marriage, that is.
The President teases Debbie Fiderer that one of the dignitaries at the wedding was the Duke of Edinburgh. The Duke of Edinburgh is Prince Phillip, husband to Queen Elizabeth II of the UK. The husband of the Queen of the UK would be more noticeable than an unfamiliar Duke, which is probably what makes the joke so funny. Next in line to be Duke of Edinburgh will be Prince Edward, the Queen's youngest son.
Kristin Chenoweth (Annabeth) appears in the church scenes towards the end of the episode, although she does not have a speaking role.