The ENQUIRER has learned exclusively that TV beauty Christina Applegate is heartbroken after her on-again, off-again boyfriend, 26-year-old Lee Grivas, was found dead of an apparent heroin overdose.

The 36-year-old Samantha Who? star is "absolutely devastated over the sudden loss," said an insider.

Grivas — a fisherman, skateboarder and aspiring photographer — died July 1.

An official cause of death has not been issued, pending toxicology tests. The death was reported as a possible accident or suicide.

The former Married.. With Children star met Grivas in 2006 while she was performing in the Broadway musical Sweet Charity.

The two began dating as her marriage to actor Johnathon Schaech unraveled, but she ended the relationship because she reportedly felt Grivas was too much of a free spirit.

A source close to Grivas told The National Enquirer: "Lee also had a long history of drug problems, dating back to his teen years. Christina broke up with him a number of times because of his struggles with getting clean. She loved him, but couldn’t stand by and watch him ruin his life."

After the lovers reunited in April, Grivas left Christina in a last-ditch bid to get sober, according to the source.

"Christina loved Lee dearly and even dreamed of starting a family with him," the insider told The National Enquirer.

"Unfortunately, Lee’s battle with drugs got the better of him. Christina is still in complete shock. He was just so young!"

For all the details on Grivas’ tragic death and Christina’s heartbreak, pick up next week’s issue of The National Enquirer.