King Charles and Queen Camilla are set to celebrate their 20th wedding anniversary on Wednesday, April 9, yet Paul Burrell—who served as butler to Princess Diana for 10 years until her 1997 death—says the monarch’s life will always be more defined by his first marriage than his current one.

As their majesties continue their tour of Italy, a royal commentator provides insight into how they have made their 20-year marriage work.