You are probably thinking of the Queen's cousin, Prince Richard, Duke of Gloucester - he's 78. He did march in the procession from Buckingham Palace to Westminster Hall, the other day.
He should be in the cortege today, but I haven't actually noticed him.
OK - just got a clear look. The Duke of Gloucester is in the cortege. So is the Earl of Snowdon who is 60, and is the late Queen’s nephew - son of her sister, Margaret.