Chris Pratt has confirmed his relationship with author Katherine Schwarzenegger, writing on Instagram: "I've cherished our time together".

The Hollywood actor and Schwarzengger, who is the eldest daughter of actor-turned-politician Arnold Schwarzenegger and broadcast journalist Maria Shriver, reportedly started dating six months ago, after Pratt split from his wife, Anna Faris.

Taking to Instagram on Friday, Pratt wished his girlfriend a happy birthday and posted a collage of photos of them together.

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He wrote: "Happy Birthday Chief! Your smile lights up the room. I've cherished our time together. Thrilled God put you in my life.

"Thankful for the laughs, kisses, talks, hikes, love and care."

It is the first time either of them has addressed their relationship publicly.

Pratt announced he was splitting from Faris, his wife of almost eight years, in August 2017.

Their divorce was finalised in October this year.

The couple have a six-year-old son, Jack