Original: Alfred's only son, also named Alfred, committed suicide in 1899, so when Duke Alfred died in 1900, he was succeeded by his nephew the Duke of Albany, the sixteen-year-old son of Queen Victoria's youngest son, Leopold.
Simplified: Alfred's only son, also named Alfred, committed suicide in 1899, so when Duke Alfred died in 1900, he was succeeded by his nephew, Charles Edward the Duke of Albany, the sixteen-year-old son of Queen Victoria's youngest son, Leopold.