Speaking exclusively to This Morning, Lyn and Ian Rigby - wearing copies of their son's medals - described the agonising 12-hour wait to find out if he was at the centre of the shocking attack.
They heard on the news that a serving soldier had been hacked to death in front of passersby at Artillery Place in the Woolwich area of London, just a few hundred yards from where Lee was based.
"Lee always used to phone me if anything had happened to do with soldiers being hurt, just to put my mind at rest," his mum Lyn said.
"I tried Lee straight away, couldn't get hold of him ... It was all over the televisions at work. I was frantic trying to get hold of him."
Although Lyn felt she "just knew", it wasn't until the early hours of the next morning that the knock on the door came.
My world just crashed ...
Lyn Rigby, Lee's mum
Lee, 25, had dreamed of being in the army since he was a little boy - even persevering through two failed attempts to get in before a recruiting sergeant discovered that he was dyslexic.
Then, with extra work to overcome that difficulty, he achieved his goal and went on to become a drummer in the 2nd Battalion Royal Regiment of Fusiliers.
He had served in Afghanistan as a machine gunner and, at the time of his death, was attached to the regimental recruiting team.
While his mum and step-dad Ian knew the risks that came with being a soldier, they never expected such harm to come to the father-of-one on the streets of London.
"I had to phone Sara (Lee's oldest sister) which was heartbreaking," Lyn recalled.
"They were very close. That was the hardest thing I had to do, to break my daughter's heart as well."
While Lyn fears that the forthcoming trial of two men accused of murdering her son will set her back, the family remain grateful for the outpouring of sympathy and support from around the world.
"We've had cards and letters from all over the world - I don't think there's a country that we've not had post from," Ian said.
"One letter arrived from Australia addressed only to 'the family of Drummer Rigby'."
Thank you for supporting me all these years. You're not just my mum, you're my best friend. So goodnight and love you loads.
Lee Rigby, in one of his last texts
Lyn added: "It's given me the strength to get through, knowing that people do care. It's given us the strength to get up in the morning."
The Royal family were among those who wrote to the Rigbys, while books of condolence were opened across the UK - including at Belfast City Hall.
In July, Prime Minister David Cameron and London Mayor Boris Johnson joined thousands of mourners at the funeral service in Bury.
Two men - Michael Adebowale, 22, and 28-year-old Michael Adebolajo - have been charged with Fusilier Lee Rigby's murder.
They are due to enter their pleas at a court hearing on 27 September, with the trial then scheduled for November.
The Rigby family have said they will be represented at the start and end of the legal proceedings.