Hayden Panettiere's ex Wladimir Klitschko honours her in heartfelt birthday tribute

Hayden Panettiere's former fiancé Wladimir Klitschko has honoured the late actress on what would have been her 37th birthday.

The Ukrainian heavyweight champion, who is the father of the late star's 11-year-old daughter Kaya, shared a photo of the Heroes actress on Instagram on Friday and wrote a heartfelt tribute to his ex.

"Instead of celebrating the way we had planned, today we celebrate her life, her spirit, and the love she brought into this world," he wrote.

"I want to thank all of Hayden's fans, friends, and everyone who has reached out for the incredible outpouring of love and support. At a time filled with so much sadness, your kindness has reminded me that there is still so much good in humanity."

The retired boxer then encouraged his followers to be kind to others and lead with love instead of hate.

"If you're reading this, I ask just one thing: even if only for a moment, think about LOVE. Reach out to a friend. Forgive someone. Be kind," he continued. "Love is a superpower. Use it."

He concluded the post, "Happy Birthday, Hayden. You are loved, you are missed, and you will never be forgotten."

Panettiere initially dated Klitschko between 2009 and 2011. They rekindled their relationship and got engaged in 2013 and welcomed Kaya in December 2014.

After the couple split in 2018, the Nashville actress relinquished full custody of Kaya amid her struggles with postpartum depression and addiction.

Days after her death on Sunday, Klitschko broke his silence on social media, stating that her death "saddens (him) deeply" and she "left this world far too soon".

"To our daughter Kaya, I will always speak of her mother with respect and make sure she remembers the person she was," he wrote. "Rest easy, Hayden. May you find eternal peace."

Panettiere's cause of death remains under investigation.