Gillen is also featured in Phenomena's 'Did it all for Love' music video although he was not involved in the actual recording of that song. After the Phenomena recordings, Gillen joined John Sykes (previously with Whitesnake, Thin Lizzy and a different band called Badlands) with the intention to form a new band Blue Murder. Gillen sang demos but parted company when Sykes decided to handle vocals himself. Gillen then contacted Jake E. Lee (former Ozzy Osbourne guitarist) to form a band. In 1988 Gillen started to form Badlands with Jake E. Lee and recruited his friend Eric Singer with whom he had played in Black Sabbath. Gillen recorded three albums ("Badlands", "Voodoo Highway", and "Dusk") with Badlands and toured from 1989 until 1992. Following his split from Badlands, Gillen stayed in L.A. and was involved with two projects. He joined forces with drummer Randy Castillo and Iggy Pop band members Whitey Kirst and Craig Pike under the name Cockfight. He also joined the band Terriff, led by guitarist Joe Holmes, fresh off his stint with David Lee Roth on the "A Little Ain't Enough" tour. Gillen rehearsed with the group for several months before moving back to his native New York. He also went to form the band Sun Red Sun with old friends. In 1993, Wilfried F. Rimensberger was planning a remake of his first Metal Hammer Loreley Festival but this time specifically to stage Phenomena's first ever live performance, with Gillen on vocals. It was going to be the launch event for a series of concerts across Europe in 1994. Gillen called from New York and told Rimensberger in Munich that he had to bow out as he was too ill to perform. Gillen died from an AIDS-related disease in a New York Hospital on December 1, 1993. He first contracted the disease around 1990, and according to his Badlands bandmate Jake E. Lee, "in between the first and the second record, he started getting really thin and didn't look quite as healthy". Lee also claimed that he had not been aware of Gillen's diagnosis with AIDS until a meeting with then-Badlands manager Paul O'Neill, who was going to tell Atlantic Records about his illness if they fired him, and Gillen reportedly said to Lee, "Well, it's not true, so fuck him. Fire him." Lee concluded, "So we did fire him.