Customers aged 18 to 93 were affected, the bank said.
The average loss to romance fraudsters was £4,500.
Santander customers lost £6,826,748 to romance scams in the 12 months running from August 2023 to August 2024.
Some £3,813,410 was lost between March and August this year.
Half (50%) of people have received unsolicited online romantic or flirtatious messages, which they suspected or have confirmed to be a scam, according to an Opinium survey of 2,000 people for Santander in July.
Nearly a third (29%) said they would offer financial help to a romantic partner they have known for less than six months.
But nearly two-thirds (65%) of people believe they would never become a victim of romance fraud.
Peter Staffell, a behavioural expert at Santander UK, said: “Scammers are experts at presenting themselves as someone you can trust, someone who ‘gets’ you.
“They play the long game, building a relationship before executing on their scam and, as our research shows, it’s a natural instinct for many of us to willingly lend a financial hand to someone who we have formed an emotional bond with.
“Then they’ve gone. The scam is complete, and the impact extends far beyond the financial losses, leaving emotional scars and often people feeling more isolated than before.
“You can take control though, a few simple checks when you first start to speak to someone, and before your emotions take hold, can reveal a lot about the person you’re speaking to and save heartache further down the line.”
Paul Gorton, a former contestant on BBC’s The Traitors, said: “In my experience, it’s surprisingly easy to build deep trust, especially when someone is charming and says all the right things.
“As we start to feel a connection, whether it’s real or not, we can end up overlooking red flags and ignore any warnings from others around us.
“Stay vigilant to spot a traitor, it’d be too easy if they simply messaged you out of the blue asking for your money. Approach any new relationship with cautious optimism, complete checks and having your wits about you at the start.”
Here are some tips from Santander to stay protected from romance and friendship scams:
1. Try to remove emotion from your decision-making. Be really careful if you are lending or giving someone money. No matter how urgent their reason might seem, it is important you think it through. Consider discussing it with a trusted friend or family member first.
2. Pictures can be edited and fake profiles can easily be made. Performing a reverse image search online can show whether the photos have been taken from another website or social media platform.
3. It could be a red flag if the person you have been talking to online will not video call or meet you in person. Fraudsters will make excuses about why this cannot happen or change plans to do so at the last minute.
4. Never send money or give card details, online account details, or copies of important personal documents to anyone you have only met online.