His oldest son King/Emperor Edward VIII.
George V was the monarch of the UK until his death in 1936
Albert was called King George VI. His father was King George V. When King George V died in 1936 his oldest son took the throne. He was King Edward VIII. Before the year was out King Edward abdicated so he could marry an American. So, Prince Albert took the throne. Sometimes monarchs change their names for certain reasons when they take the throne. Albert decided to call himself King George VI as a "continuation" of his father's reign.
George V
The king in the UK was George V.
George V
in UK: George V Edward VIII & then George VI
King George died on the evening of January 20, 1936. His oldest son, Edward, took the throne as Edward VIII. He abdicated on December 11, 1936 to marry a foreigner, which a monarch can't do. So, Prince Albert took the throne and changed his name to King George VI in honor of his dead father.
Unfortunately, King George had no sisters named Mary, so no she was not in line for the throne.
George V was on the throne at the first Commonwealth Games in 1930.
In 1865 Queen Victoria was Queen of the UK. Her oldest son, Prince Albert Edward of Wales, was next in line to the throne. That year Prince Edward had his second child, George, was born. His older brother, Prince Albert Victor, was second in line to become King after his father. But, in 1892 Prince Albert Victor became sick and died. This boosted Prince George to second in line after his father. In 1901, Queen Victoria died and Prince Albert Edward took the throne, calling himself Edward VII. This made Prince George the Heir to the throne. In 1910 King Edward died and Prince George took the throne.
King George V was succeeded by King Edward VIII who abdicated and became the Duke of Windsor and, Edward VIII was succeeded by his brother, King George VI.