Kelly Osbourne is mourning the loss of her father Ozzy following his death on Tuesday. Osbourne posted a brief message to her Instagram stories on Thursday afternoon. “I feel unhappy I am so sad,” she wrote. “I lost the best friend I ever had.”

Osbourne died on Tuesday at 76, just weeks after he and Black Sabbath performed at their farewell Back to the Beginning concert earlier in July.

Osbourne, who battled Parkinson’s before his death, sat onstage in a black leather chair as he performed for the 42,000-person crowd. He sang five songs by himself, before he was joined by his former bandmates for four Black Sabbath songs.