Despite the serious subject matter, comedian Russell remained jovial.
"Well that's just silly," he tweeted, alongside a photo announcing he was giving a UN press conference.
He later posted a link to an story about his stance on drugs, writing: "An article that tells us why we need to change drug laws. (And a photo that tells us I need to change hairdressers)."
Russell's appearance in the Austrian capital comes two weeks after he cancelled a sold-out show to be by his mother's side following her diagnosis with breast cancer.
Russell Brand cancels show after mum Barbara is diagnosed with breast cancer for second time
The Essex-born star had been scheduled to perform at the Warwick Arts Centre on 6 March and the Derby Assembly Rooms on 7 March, but made the decision to postpone the events in order to be with his family.
At the time Russell took to Twitter to apologise to fans, explaining, "My mum ain't well".
He later expanded on the reason during his YouTube show The Trews.
"My mother has currently got breast cancer," he said in his video blog, while speaking of his dismay that the NHS is "being destroyed" by cuts.
Barbara, who has a very strong bond with her son, successfully battled uterus cancer when Russell was eight years old, and breast cancer a year later.
Russell often pays tribute to her for her bravery and love, in no small part because his parents split when he was just six months old and she raised him as a single parent.
It's a little princess!