The girlfriend of sports broadcaster Clinton Grybas has described his sudden, unexplained death as the worst day of her life.

Laurenna Toulmin choked back tears on radio on Monday as she recounted the "best four years of my life" as Grybas' partner and how the couple planned to marry.

Grybas, who died at the weekend, and Ms Toulmin met at Melbourne radio station 3AW, where he worked as a sports presenter and she a producer.

"Clinton walked into the studio for his sports segment on a Friday and straight away I just thought, oh my God, who's that?" Ms Toulmin told Fairfax Radio.

"Just instantly - the cliche, love at first sight, I suppose."

The pair spent more than six months harbouring secret crushes and sussing each other out before they hooked up at a Grand Prix party.

"We started talking and it was just like everyone else at that party didn't exist and we were together for the rest of that night and ever since."

Ms Toulmin said she and Grybas kept their relationship a secret in the beginning but more recently colleagues were pushing for an engagement ring.

"It was coming too," she said.

Grybas' parents Vic and Sandra believe their son was planning to propose to Toulmin this year, possibly during a pre-football season holiday on Hayman Island in the Whitsundays.

Grybas, 32, was found dead in his 15th-floor Southbank apartment on Saturday after failing to show for 3AW's Sports Today program, which began at noon (AEDT) that day.

There is speculation he may have fallen and injured himself while sleepwalking.

Ms Toulmin said she was shopping in Ballarat for a barbecue for their apartment the day Grybas died and described her panic at not being able contact him and learning he had not showed up for work.

"(It was) the worst day of my life," she said.

Ms Toulmin prayed her boyfriend had just slept in but her worst fears were realised when a neighbour broke into the couple's apartment with building management.

"They got in and she (the neighbour) said, 'I can see him lying down ... is it okay if we go over and shake him?'

"I said yeah that's fine ... be careful he might get startled though.

"And she said, 'he's not breathing'."

Ms Toulmin said Grybas would often surprise her with gifts and was dedicated to his work, perusing weeks worth of newspapers and sports programs on his return from holidays.

She thanked the public for their kind wishes, assuring listeners Grybas' broadcast manner was not a put-on.

"In real life he was even better, he was amazing, loving, the most beautiful person.

"I loved him so much ... that was the best four years of my life, I just don't know where to go from now."

Listen to her interview here (3AW)