Complex sentence: Albert's body was temporarily entombed in St. George's Chapel, Windsor Castle, and and a year after his death his remains were deposited at Frogmore Mausoleum, which remained incomplete until 1871.
Split into simpler sentences: Albert's body was temporarily entombed in St. George's Chapel, Windsor Castle. The mausoleum at Frogmore, in which his remains were deposited a year after his death, was not fully completed until 1871.