Mendorax Dellora

Mendorax Dellora was a human colony planet which; by the year 5343, was ruled by King Hydroflax up to his demise. (TV: The Husbands of River Song)

Astronomical data
The surface of the planet appeared to be Earth-like, blanketed with ice and snow, littered with large stretches of forest and an oxygen-rich atmosphere, apparently capable of sustaining human life.

The planet had two large blue moons visible within its atmosphere. (TV: The Husbands of River Song)

History
When River Song called for a surgeon, to in fact remove Hydrofax' head, her assistant Nardole mistook the Twelfth Doctor for the one he was looking for, and brought him along to help. It was here that River first met the twelfth incarnation of the Doctor, although she was not privy to his identity until later on, on the Harmony and Redemption. (TV: The Husbands of River Song)