Chris Hemsworth's son Tristan called his dad his "special friend" in a cute handwritten note.

Chris Hemsworth and Elsa Pataky

Chris Hemsworth and Elsa Pataky

The 37-year-old actor took to Instagram to share a picture of his six-year-old boy's sweet message he penned for a school writing project.

Tristan - who is a twin to brother Sasha - wrote about his favourite activity to do with his father, swimming in the pool, and melted the 'Avengers: Endgame' star's heart.

The note reads: "My special friend is dad, together we go in the pool, together they make me feel happy."

And his teacher added in green pen: "Well done Tristan."

Chris - who also has eight-year-old daughter India Rose with his wife Elsa Pataky - added the loudly crying emoji and a red heart in the caption to express being overwhelmed with emotion by the touching tribute.

Meanwhile, Elsa previously revealed the celebrity couple - who in Byron Bay in Australia - have managed to encourage their kids to embrace the outdoors with them amid the COVID-19 pandemic.

Elsa said: "We've got the kids into surfing.

"Any hobbies to get them outside, and not on social media and computers. My daughter has been horse riding with me since she was two-and-a-half."

The 44-year-old model also admitted her relationship with the 'Thor' star requires "constant work".

The pair have been married since 2010, but she dismissed the idea that their romance is "perfect", admitting they've experienced their fair share of ups and downs over the years.

She shared: "It's funny that people think of us as a perfect couple. No way.

"It's been ups and downs, and we still keep working at the relationship. I think a relationship is constant work. It's not easy."

Despite this, Elsa always retains a positive attitude towards their relationship, and revealed they've bonded over their love of the outdoors.

She said: "[Chris and I] love to do sports, eat healthy and move our bodies."