The US president didn't come close to selling out the 19,000-capacity arena in Tulsa, Oklahoma.
The singer has been using her Instagram page to speak out against racism and support the protests decrying police brutality against Black people.
The former motocross champion said both Pink and their son Jameson had been "extremely sick".
The US singer admitted she had "never prayed more in my life" as she and her son fought the virus.
The US singer revealed she had tested positive for Covid-19 but has since recovered.
Aussie stars Kylie Minogue and Naomi Watts have also spoken out about the fires that are raging across their home country.
"Can’t wait to see the woman you grow up to be. I have a feeling you are gonna be strong, fierce, compassionate, and caring."
The US stars have joined Sir Elton in backing the royal couple after he hit out at “distorted and malicious” press reports.
Is it safe for children under 16 to use hair dye? We asked an expert.