Harry attended three engagements without Meghan, before the Duchess joined him for a walkabout on Fraser Island for the final engagement of the day.
The royal aide said: “She isn’t sick, she just had a tiring few days and we were concerned about the roads on the island which are incredibly bumpy and uncomfortable for anyone, let alone a pregnant woman.
“But the duchess was very keen to re-join the duke at the last engagement of the day to greet the people of the island.”
Meghan held her baby bump as she met well-wishers with Harry. The 37-year-old wore a striped dress by Reformation which featured a daring thigh split for the outing.
The couple, who wed in May, were given gifts including flowers and bears.
One royal fan greeted the Duke with a sign reading “Rangas rule”, an Australian slang reference to Harry’s ginger hair.
Nine-year-old Jada Quinn said: “My dad is a ranga and I’m a little bit a ranga and he appreciated the sign.”
A royal aide has issued a statement over Meghan Markle’s pregnancy
Meghan joined Harry for a walkabout on Fraser Island
Meghan held her baby bump as she met well-wishers with Harry
The walkabout comes after doting Harry reportedly told Meghan to “pace herself”, following a late night on Saturday at the opening of the Invictus Games.
A source said: “She is not sick, just tired.”
“We have to try to pace her. We have to make sure she is well paced and not overdoing it.
“She had a very late night last night.
“She wants to do everything, but Prince Harry is encouraging her to pace herself.
“We want to make sure she gets enough rest at the beginning of the day and at the end of the day.
“If it has been a very late night due to unforeseen circumstances, we have to adjust for that.”
Kensington Palace previously revealed that Meghan would pull out of a number of engagements during the 16-day tour.
Kensington Palace said: “After a busy programme, The Duke and Duchess have decided to cut back The Duchess’s schedule slightly for the next couple of days, ahead of the final week-and-a-half of the tour.”