Social media users are rallying round TV personality Timmy Mallett to help find his missing bike.
The star recently celebrated completing a 2,500-mile charity ride across Europe in memory of his late brother Martin.
Mallett, 62, was drinking with friends on Friday when the bike was apparently taken from a pub in Cookham, Berkshire.
He told the Press Association it would be "the loveliest thing" if the bike could be returned on Wednesday, which would have been Martin's 65th birthday.
I've cycled half way across Europe on my Giant E bike carrying dear brother Martin's memory— Timmy Mallett (@TimmyMallett) August 4, 2018
Securely locked in my local pub car park last night it was taken.
CCTV shows them.
Heartbroken#findTimmeeeeEbike@bikeregister@GiantUK @MaidenheadAds @ThamesVP @TVP_Maidenhead pic.twitter.com/bpPQBPwk55
The former Wide Awake Club presenter is offering a "substantial reward" for the Giant E bike's return.
He said: "The irony is so awful. You can take it all over the world, and yet at home it was not safe at the local village, in the lovely local pub.
"I'm heartbroken," he continued. "It's more than just a bike to me. This bike I've cycled with 2,500 miles, halfway across Europe.
"I left in the depths of winter and it took two months. I was on my own and my bike was my best pal along the way, the only thing I could absolutely rely on. I'm devastated to lose something so special."
Thames Valley Police have tweeted to say they are "on the case", while hundreds of Twitter users have offered to help the star.
@TimmyMallett - Hi Timmy. We are on the case 🚨👮♀️👮— Thames Valley Police (@ThamesVP) August 6, 2018
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Mallett had just finished the Camino de Santiago trip in memory of his brother, who had Down's Syndrome, when the bike went missing.
The route is a pilgrimage across Europe, ending in north-west Spain.
"I'm not looking for retribution," Mallett said. "I don't know the circumstances of the people who took it. I'm appealing to somebody's good nature to do the right thing.
"Every day on the pilgrimage you are vulnerable because you wake up each morning not knowing where you are going to stay the night, who you are going to meet, what is going to happen, and you are on your own, and every day the bike delivered.
"There's a possibility that someone who knows where the bike is has enjoyed my TV shows over the years and would like to reunite me with it."
The presenter travelled across three countries in two months, leaving some of Martin's personal items at places along the route.
He created more than 100 paintings on the trip, receiving backing from the Prime Minister Theresa May and the Duke of Cambridge along the way.
The bike ride did not set out as a tribute to Martin but became so when he died just before the trip was due to begin.