Nicholas Lyndhurst and his wife Lucy marked a heartbreaking milestone on Tuesday - their late son Archie's 21st birthday.
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In honour of the occasion, Lucy took to Instagram to share a loving message for her son, along with some unseen family photos - prompting an outpouring of love and support for the couple.
WATCH: Archie Lyndhurst's girlfriend and friends mark his 20th birthday days after his death
Lucy poignantly wrote: "Today 4th October will always be the best day of our lives. The day you arrived and completed us. Every adventure has been amazing and utterly joyous, we can never thank you enough for the tremendous ride.
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"Today is your 21st birthday. A day we'd talked about for years and the plans you had for it. I wish more than anything your story and adventures could have continued. You deserved so much more. You only ever gave to the world. I shall never understand why. Never.
Lucy paid a loving tribute to her son on his 21st birthday
"We now live in a world we no longer understand and maybe it doesn't understand us either. But our love for you still grows as it always did. That will never diminish."
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Lucy - who has been married to Only Fools and Horses star Nicholas since 1999 - continued: "The pain of not seeing you every day or hearing your voice and your laughter is absolutely agonising.
Archie tragically passed away shortly before his 20th birthday
"We think about you night and day. You are the best son anyone could wish for. A parents' dream. I always said you were only on loan to us. I just didn't realise how short a time we had.
"You didn't waste a second though. You charmed so many people's lives, they are the lucky ones who got to know you. We love you beyond measure and hope you like what we are doing to honour you today. 'Big Love' darling boy. To the moon and back and beyond. 'In a Bizzle' M & OM XxX."
Archie was the couple's only child
Archie tragically passed away in his sleep on 22 September 2020 from a brain haemorrhage caused by a condition called Acute Lymphoblastic Lymphoma/Leukaemia.
Lucy said at the time that she and husband Nicholas were assured by the doctor who explained the post-mortem results to them that there "wasn't anything anyone could have done as Archie showed no signs of illness".
She said it was "not leukaemia as we know it" and that acute in medical terms meant "rapid". The couple were "utterly floored" to think something like this could happen, she wrote, adding: "It's very rare and around only 800 people a year die from it."
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