Confirming the break-up on Twitter, Guy told his 5,000 plus followers that the couple had in fact called time on their relationship in January.
"Rumours r true I'm afraid – Kate and I parted ways back in Jan. Sorry 2 be boring but we couldn't be closer. We'll love each other 4 ever xx," he wrote.
Kate Mestitz and Guy Pearce met when the former Neighbours star was 12
Guy followed up the post with two photos – one of the couple in their happier times and another of his estranged wife. "The best 20+ years of my life – with this beautiful lady.....," he wrote alongside a picture of Kate.
Guy, 48, also released a statement through his spokesperson, writing: "Kate and I will always love and support one another and be the best of friends. No-one knows me like Kate does, and we'll forever be appreciative of our mutual respect. We've both grown enormously through our relationship, but sadly, the time has come to part ways."
The best 20+ years of my life - with this beautiful lady..... pic.twitter.com/EQc3dl1FpR— Guy Pearce (@TheGuyPearce) October 12, 2015
"No-one knows me like Kate does," wrote Guy in a statement
The pair met when Guy was just 12. They lost touch but then crossed paths again in their late teenage years, and fell in love. They married in March 1997.
In a candid interview with The Guardian, Guy spoke about their relationship dynamics and his reluctance to have children.
"I don't even need them," the actor said. "There are enough babies in the world. Besides, I don't think I would be good for babies. I'd be on and off. I think they need more consistent affection than I would be able to give."
Rumours r true I'm afraid - Kate and I parted ways back in Jan. Sorry 2 be boring but we couldn't be closer. We'll love each other 4 ever xx— Guy Pearce (@TheGuyPearce) October 12, 2015
"We are emotionally honest with each other," he added of his and Kate's bond. "We can be hard work. Other couples always say, 'Let's not invite Guy and Kate, they're not much fun to be around.' We're not very bouncy."
The actor was born in Cambridgeshire but moved to Australia when he was just three years old. At the age of 18 he landed a role on popular soap opera Neighbours, starring as Mike Young. Guy has also appeared in Home and Away, The King's Speech and Prometheus among other films and TV shows.