Matt Shirvington named new Sunrise co-host

"It was the worst kept secret," he said during the show.

"(I have) mixed emotions, just amazing, daunted, so excited, happy, cannot tell you the honour and privilege this is Kochie particularly, a huge job and an exciting job."

The former sprinter has been a regular fill-in for Koch on Fridays, which he said served as good training for his new role.

It follows Koch's departure announcement after 21 years on-air.

Initially filling in for a sick colleague, Koch landed in the host chair in 2002 at a time of rapid experimentation in the makeup of Seven's morning TV.

Koch has co-hosted more than 5300 shows over the years alongside Melissa Doyle, Samantha Armytage and most recently Barr.