Hi Rebecca, Which royal family are we talking about? There are several, you know! If it's the British, all the suspicious deaths I know of occurred during medieval times and earlier. (Because this was before the Scottish and English thrones were joined these were Kings of England, not Britain.)
The Princes in the Tower. Edward V and his younger brother Richard. Kept prisoner by their uncle Richard (later King Richard III) and presumably murdered on his orders, around June-September 1483. George Duke of Clarence, Richard III's older brother, was believed to have been killed in the Tower of London, on his brothers' orders.
William Rufus, King William II. He was killed by an arrow in a hunting accident in the New Forest in August 1100. It may have been an accident, but it was regarded as suspicious at the time, and his brother Henry lost no time in arranging a quick coronation for himself, as Henry I.
Edward II seems to have had homosexual leanings and was also regarded as a weak King . He was held prisoner in Berkeley Castle, Gloucestershire, after his estranged wife and her powerful lover Roger Mortimer forced his abdication in favour of his young son. Edward's murder was arranged by Mortimer, by means, it was said, of a hot poker thrust into his bowels, in September 1327.
Richard II was imprisoned by the forces of Henry Bolingbroke (future King Henry IV) and was forced to abdicate in 1399. It is believed that Richard was starved to death in Pontefract Castle in the early months of 1400. There's no evidence of physical murder, but he was killed by neglect.
Henry VI was involved in several rebellions in his reign and was twice deposed during the Wars of the Roses. Henry suffered from mental problems. He was believed to have been stabbed to death in the Tower of London while a prisoner there in May 1471. It's not known who his killer was. It was probably someone acting on the will of the Yorkist King, Edward IV, who replaced Henry on the throne.
