The ceremony, which is taking place this afternoon at St George’s Chapel in Windsor Castle, will be attended by a maximum of 30 people in line with government guidelines.
The Duke of Sussex flew in from Los Angeles to London last weekend for the occasion.
Meanwhile, Prince Harry’s wife, Meghan Markle, and their son, Archie Harrison Mountbatten Windsor, did not join him.
Meghan had been “hopeful” to attend, but was not cleared for travel by her doctor due to the stage she is at in her pregnancy.
The couple revealed that they were expecting a girl in their interview with Oprah Winfrey last month.
While a specific due date was not mentioned during the interview, Meghan confirmed it would be in the summer.
According to the NHS, most women can travel safely “well into their pregnancy”.
“Travel during pregnancy is a concern for many women,” says Sarah Reynolds, a consultant obstetrician and gynaecologist at the Bedford Hospital NHS Trust.
“But if your pregnancy has no complications then there’s no reason why you can’t travel safely, as long as you take the right precautions.”
The organisation adds that after week 28 of pregnancy, some airlines may ask for a letter from your doctor or midwife confirming your due date, and that you aren’t at risk of complications before clearing you to fly.