Heartbroken KATEY SEGAL is picking up the medical bills of her ex-husband – who’s battling deadly prostate and bone cancer, The ENQUIRER has learned.

The couple divorced 10 years ago, but pals say Katey – a Golden Globe winner for her role as a tough motorcycle mama on the FX hit Sons of Anarchy AND for voicing Leela on hit toon Fututrama – didn’t hesitate to help her ex, musician Jack White.

"When Katey learned of Jack’s dire condition, she found him a specialist and she’s footing all his medical bills," divulged a friend.

"She realizes Jack’s prognosis is grim, but she’s deeply committed to helping and caring for him. She’s been his main support both emotionally and financially."

The couple had two children together- Sarah, now 16, and Jackson, now 15 – during their seven-year marriage.

Jack has not remarried, but Katey, 57, has moved on to a new life with husband Kurt Sutter – creator of the outlaw biker drama "Sons" – and their daughter Esme, 4, who was born via surrogate.

But she’s "always had a place in her heart for Jack," the friend said.

In 2000, the hard-partying drummer credited his then-wife for saving his life by getting him into multiple rehab stints for addictions to alcohol and painkillers.

"I’ve been an alcoholic for 18 years," Jack admitted to The ENQUIRER. "Katey was concerned. I didn’t feel safe around my kids. I didn’t like what was happening to me."

While 56-year-old Jack makes his home in Nashville, he often travels to Los Angeles to see the former Married…With Children beauty and their children.

"Jack is incredibly grateful that Katey still cares for him and is willing to make sure he gets the best medical treatment," said the friend.

"Katey will never turn her back on Jack."