You'd expect the first song written for any Van Halen album to be a blazing rocker. Not so with 1988's OU812.

In his 2011 memoir Red: My Uncensored Life in Rock, Sammy Hagar recalls being picked up by Alex and Eddie Van Halen at the Los Angeles airport after returning from a promotional trip to Japan for his 1987 solo project, I Never Said Goodbye (which Eddie co-produced).

"'We want you to hear something,' Eddie said. They played me the keyboard part for 'When It's Love,'" Hagar wrote. "I was covered in goose bumps. That was almost the inspiration for the whole album. We knocked that song out and knew we had something."

They weren't wrong. Released in June 1988 as the second single from OU812 – Van Halen's second album with Hagar fronting the band – "When It's Love" hit No. 1 on the Billboard Mainstream Rock Chart and became the group's third, and final, Top 5 entry on the Billboard Hot 100. It was also ranked one of VH1's 25 greatest power ballads, while Eddie Van Halen said that the song's guitar solo was homage to Eric Clapton.

Watch the Music Video for Van Halen's 'When It's Love'

The idea of a Van Halen power ballad might have seemed disconcerting to fans during the David Lee Roth era, but Hagar ushered in the concept on 1986's 5150, with singles such as "Dreams" and "Love Walks In."

Ironically, the sweet sentiment of "When It's Love" came at a time when Hagar's own love life was starting to unravel: His first wife Betsy, whom Hagar married in 1968, had started battling anxiety and mental health issues, at one point requiring 24-hour in-home care. The couple divorced in 1994.

The popularity of "When It's Love" was also bolstered by a music video, shot between tour dates and featuring Van Halen performing in a bar – bassist Michael Anthony plants a kiss on Eddie Van Halen's cheek at one point – while a couple slow dances to the song. Hagar wrote that he "blew out my voice" during the 12-hour shoot, but he also "really connected" with the actress from the dancing couple, though he "never got the chance all day to take her to the back room."

In addition to OU812, "When It's Love" is also featured on 1993's Live: Right Here, Right Now and on the 2004 compilation The Best of Both Worlds. It was also one of the vintage songs Gary Cherone performed during his short tenure with the group following Hagar's 1996 departure, and Hagar has included it in solo concerts over the years.

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