Alphonse was a worker on the planet Darillium.
When the starship Harmony and Redemption crashed on the planet, he scanned the area for survivors, but couldn't find any. He was approached by the Twelfth Doctor, who told Alphonse he should build a restaurant atop the site of the crash, in the view of the Singing Towers.
Alphonse told the Doctor it would cost a lot of money to build, and the Doctor promptly gave him the Halassi Androvar, explaining that there was a huge reward for its return and Alphonse could use that money to build the restaurant. He later did, with his restaurant being so popular that tables were booked four years in advance. (TV: The Husbands of River Song)
Behind the scenes
Alphonse is not explicitly named on-screen, but the actor who played the character, Chris Lew Kum Hoi, is listed as "Alphonse" in the closing credits.